A Winnipeg cannabis advocate and head shop owner does not think Manitoba's ban on homegrown cannabis will deter people from growing plants when recreational marijuana is made legal this fall.

The federal government announced this week it will allow Canadians to grow up to four marijuana plants at home for recreational purposes. Despite this, Manitoba, Quebec and Nunavut still plan to ban home cultivation and Canada's minister of justice said the federal government doesn't intend to challenge provincial laws.

Jeremy Loewen, owner of Hemp Haven, calls Manitoba's ban a tax-grab and says it's not likely to stop people.

"You've got a whole bunch of illegal growers already," Loewen says. "It's not going to deter them and especially for the people that are doing three, four plants or something like that."

Loewen says when weed is made legal, he suspects those who do get arrested for growing pot will contest the charge in court.

"I think [the province is] just wasting their time, wasting everybody else's time and looking foolish in the process," he said.

Provincial charges comes with real risks, lawyer says

However, University of Manitoba law professor Karen Busby said growing pot in Manitoba could come with real consequences.

"The province can make it an offence, which technically speaking isn't a criminal offence, but practically speaking has the same effects," Busby said. "So you're taking a chance."

If charged and convicted, individuals may be subject to fines and having to declare that offence when crossing the border into the United States, she said.

"You could challenge the constitutionality of the law in court, if you want, but that's a lot of money and a lot of time and probably not something that a regular Manitoban wants to spend their time on."

Court challenge not clear cut

There are also no guarantees a constitutional challenge will be successful, Busby said.

"It's impossible to say [who would win]. Fifty per cent of lawyers would say, yes the province would be successful. Fifty per cent would say the Feds would be successful," Busby said.

"It's kind of in the sweet spot of ambiguity around provincial, federal regulation."

In order for a constitutional challenge to be successful the question that has to be answered is whether the provincial law gets in the way of, or "frustrates the purpose," of the federal law, she said — in this case, getting pot sales out of the hands of criminals.

"If the purpose of the federal law is to shut down the black market, and a key aspect is to allow people to grow at home, then a challenge to the provincial law should be successful," said Busby.

However, if it it can be argued that is not a serious goal of the federal government then the provincial law could be upheld, she explained.

There are many other examples where federal and provincial laws overlap, including laws around surrogacy.

The federal government allows Canadians to engage in surrogacy, whereby a woman agrees to carry a pregnancy for another person, so long as it's done without pay, Busby said. However, Quebec law prohibits surrogacy.

"There's never been a constitutional challenge," Busby said. "But you see that again, that's one of those cases it's in the sweet spot. It's right in the middle. Can the province do that? Does that frustrate the purpose of the federal law?"

Busby said she suspects within a year or two of cannabis legalization a Manitoban charged with a provincial offence involving cannabis will have the "interest and wherewithal" to pursue a constitutional challenge.