It has been known for some time now that Markstrom was looking to leave the Flames. He went so far as to request a trade from the team last season, and while it sounded like he was as good as gone, the deal never came. At the time, he was linked to the New Jersey Devils, and that seems to have followed him to this summer, as it was the Devils who ultimately acquired the veteran netminder.
According to NHL insider Elliotte Friedman, the Toronto Maple Leafs had a similar offer on the table for Markstrom. One could imagine that deal probably looked something like a 1st round pick and perhaps a player like Timothy Liljegren. However, the Flames picked New Jersey's offer, likely because they did not want to trade with their own former GM in Brad Treliving.
This is not that surprising. After all, the Leafs were also reportedly interested in Chris Tanev and Nikita Zadorov last season, but they lost out on both of those players too. As such, it seems like the Leafs will not be completing a trade with the Flames anytime soon.