Frogs of Quebec- http://www.google.ca/url?sa=t&rct=j&...48340889,d.aWc

It looks like a Rana clamitans. A bullfrog would also be possible but it looks like it has the beginings of the dorso-lateral folds, the little ridges running down the sides of the back, which would rule out bullfrog. Given the stage it's in, you should know one way or another pretty soon as these folds are typically pretty obviously present or absent by the time it crawls onto land. Both species will spend over a year as a tadpole so you will find large tads like this early in the year.

A mink frog may be another candidate, I've little experience with them as tadpoles, but as adults they are very similar to green and bullforgs.

Checking the area you found it in for adult frogs can also be handy for ID of tadpoles.