For weeks, as the Mets slogged along in a going-nowhere season, fresh trade rumors involving their young starters had become the norm. The question was no longer if General Manager Brodie Van Wagenen would start rebuilding but when the process would begin.

No scenario was unthinkable: Even the idea of swapping with the Yankees, whose rotation is in crisis, was credible.

On Sunday, things turned upside down as the Toronto Blue Jays agreed in principle to send Marcus Stroman, an All-Star right-hander, to the Mets for two top prospects, according to a person familiar with the details of the trade who was not authorized to discuss it publicly.

The deal caught much of baseball by surprise. The Yankees were said to be deep in talks for the dynamic Stroman, who is both familiar with the local market (he is a Long Island native) and on a notable hot streak (2.96 E.R.A. since May 11).