Not much can, or should, be determined about the Giants yet, even after they snapped their five-game losing streak on opening day.

Heck, they haven’t even played a game at home. That comes Sunday at MetLife Stadium, and at around 1 p.m., the answer to the most serious question should come into greater focus.

The theme and overlying goal of the offseason was to fix the broken defense. Coming back then holding on to beat the Cowboys, 20-19, offered a few glimpses as to what $200 million in free-agency spending, added to what looks to be smart selections in the draft, can do to revitalize a defense. Three or so hours of football against the Saints will tell a whole lot more.

“Preparing for a rookie is easy, because they have a limited playbook,’’ cornerback Janoris Jenkins said. “With Drew Brees, he has an open playbook. To changing all the routes and switching plays, and seeing matchups he doesn’t like, and attacking — I think that’s a big difference.”

It is a big, big difference. Dak Prescott may grow up to have a fine career with the Cowboys, but in the here and now, he is a rookie, and the Giants were able to exploit his inexperience. Brees, well, that is a different species of quarterback, and every level of the Giants’ defense will be stretched to the limit to hold him down.

The last three times Brees beat the Giants, the Saints have scored 48, 49 and 52 points, and there is a reason just five players on defense from last season’s wild 52-49 loss in New Orleans will start for the Giants in this game.

It doesn’t help that the Giants have concerns about defensive ends Jason Pierre-Paul (shoulder) and Olivier Vernon (wrist).

The Saints are far from the best team in the league, but their passing attack is probably the toughest to defend. They lost their opener to the Raiders, 35-34, yet Brees threw for 423 yards and four touchdowns. Two receivers — Willie Snead (172 yards, one TD) and Brandin Cooks (143 yards, two TDs) — made their fantasy football owners quite happy.

Last season’s Nov. 1 scoring spree was outrageous, but it often turns into that sort of game when the Saints are around. It figures to be sticky and rainy, and that could slow down the air show.

“You have to expect that they’re going to be able to score just because they have that ability,’’ Eli Manning said. “A bunch of times when we’ve played them, it’s been high scoring. We have to know that offensively and do our part. We have to protect the football, sustain drives and convert on third downs. We have to do our part, make sure we’re scoring touchdowns and put us in a position to win.’’

Marquee matchup

Saints WR Brandin Cooks vs. Giants CB Janoris Jenkins

After a breakout 2015 season (84 receptions for 1,138 yards and nine TDs) Cooks picked up where he left off, embarking on 2016 with a six-catch, 143-yard outing against the Raiders, including two touchdowns — one a 98-yarder. He is a 5-foot-10 dynamo and should be a different challenge for Jenkins — who, in his Giants debut, blanketed bigger, more physical Dez Bryant (one catch for eight yards).

This is an entirely different deal for the cornerback called Jackrabbit. Last week, the game plan did not call for many down-the-field throws for Cowboys rookie Dak Prescott. This week, it is all systems go in the passing game with Drew Brees at the controls, meaning Jenkins will be tested, early, often and repeatedly.

4 Downs

The duel: It only seems as if the NFL is now filled with young gunslingers and that nearly every team is starting a rookie quarterback. There are some old-timers left, but showdown such as this is becoming increasingly rare. Eli Manning is 35 and in his 13th season. Drew Brees is 37 and in his 16th season. These are two of the most prolific quarterbacks in league history. Brees says his strategy is “just hang on as long as you can’’ and admits he does not have an end in mind.

“Three years ago, I said I could play for another 10 years,’’ he said. “I don’t know if that’s going to be the case, but I don’t think it will be because physically I can’t. It’s just a matter of how long do I want to play for. If I’m having fun playing at a high level and am able to stay healthy, I’ll play as long as I can.’’ As for Eli, Brees said, “He’s still going at it just like I am.’’

The mismatch? Much has been made of the Giants’ triumvirate of Odell Beckham Jr., Sterling Shepard and Victor Cruz going against an incredibly inexperienced group of Saints cornerbacks. The best corner, Delvin Breaux, broke his leg last week, leaving the Saints with P.J. Williams, Ken Crawley and De’Vante Harris, who all made their NFL debuts in the season-opening loss to the Raiders. Newly signed veteran Sterling Moore might be available but this is an extremely untested corner situation. Dwayne Harris caught two touchdown passes for the Giants last season vs. the Saints but is not a big part of the offense this year. Harris, though, sees what everyone else sees.

“They definitely got a lot of young guys who haven’t played a lot of football in the National Football League,’’ Harris told The Post. “I think that gives us the advantage. You got guys like Victor Cruz and Odell and then you got a young guy, Sterling Shepard, who is coming along … this is a tough task for them, you know? This is our opportunity to take advantage.’’

Stay the course: There were massive defensive breakdowns by the Giants in last year’s scoring-fest, as Brees threw touchdown passes of 34, 26, 53 and 21 yards. On a 34-yard scoring pass to Willie Snead, safety Landon Collins bit on a flea-flicker, leaving himself trailing badly in coverage. “Now, he’s not a rookie anymore, so I don’t suspect that will happen to him again,’’ defensive coordinator Steve Spagnuolo said.

The Giants know Brees will put up big numbers — since 2006, he leads the NFL in passing yards and touchdown passes — and they at least want to make him earn his way down the field. That means they must make the big play when they have it, unlike Dominique Rodgers-Cromartie whiffing on what should have been a sack last week.

“We call it ‘don’t miss the layup,’ ’’ Spagnuolo said. “He missed the layup on that one.’’

Slow it down: On the surface, it sounded like a strange question to offensive coordinator Mike Sullivan: Can you score a touchdown too fast? Last week, the Cowboys held the ball for 8:25 and 7:58 on two drives, and the Giants countered with a four-play, 75-yard touchdown drive that took just 1:33. Playing keep-away with Brees might be the best way to slow him down, but that is not the Giants’ way — unless they can control the ball on the ground with Rashad Jennings and Shane Vereen. Jennings (4.2 yards per carry) and Vereen (6.3) both had some strong moments in the opener.

“I think there’s a lot of noise about our offensive line out there,’’ coach Ben McAdoo said. “I’m confident in those guys. When you go back the last five weeks in regular season games, Rashad Jennings is the leading rusher in the league. He has the most 10-yard runs in the league, 10 yards or more. I’m confident in those guys.’’

Since Week 14 in 2015, Jennings leads the NFL in rushing yards with 507 and, more surprisingly, in runs of more than 10 yards with 15.

Paul’s pick

Give Drew Brees points at your own peril. If the Giants can contain this rarefied passing game, kudos to them and the defense can stake its claim as rebuilt. Sure, Eli Manning is going to look to exploit the young New Orleans corners, but the more the ball is in the air, the higher the chances of tips and deflections and turnovers — especially if it is wet.

Giants 31, Saints 27