I wouldn't do either. If you really want to economize, buth in terms of time and money, you'll put JFK right out of your head and concentrate on LGA-Florida only. Sure, you get more miles per dollar on the California runs, but the transfers are a hassle and they take a long time.

Here's the thing: You can't avoid an overnight... somewhere between leaving YYZ and returning, you will be spending the night somewhere, either NYC or FLA. FLA is way cheaper.

Your options are:

YYZ-LGA-FLA-LGA-FLA (overnight) LGA-YYZ

or:

YYZ-LGA-FLA-LGA-FLA-LGA (overnight) YYZ

You can't avoid it. Even if you fly out of YYZ the night before you start your runs your second roundtrip back into NYC will land long after the last YYZ-bound AC flight has left.

The only way you avoid an overnight is by doing back to back red-eye runs to California (brutal) which are only possible out of JFK ($$).

Your best case scenario is option A with a cheap Priceline hotel stay in Florida. NYC hotels are very expensive.