I'm planning a trip later this year that would go from KANJ (Sault Ste
Marie, MI) to KART (Watertown, NY), IFR and mostly through the
Canadian airspace, in a U.S. registered single engine Grumman. Going
IFR is mostly to make the two border crossing easier. I have
previously overflew Canadian airspace IFR with much shorter distance
between Buffalo and Detroit.

The flight planning software suggested the route of SSM . WALAC .
YVV . YMS . YSO . YCF . PERTH . KART. There's quite a bit of dog leg
in the middle. What're the chances for Toronto center letting me go
YVV direct YSO, and YCF direct KART? Would VFR be a better choice?
My only concern about the VFR is for them to somehow lose my flight
plan and I have to convince the U.S. controller that the flight does
not stop in Canada (therefore does not need to clear custom upon
landing at Watertown NY).

Alternatively, I can go from KANJ to KBUF (Buffalo, NY), cross the
Canadian airspace that way. The IFR route would take me right above
Toronto international airport at my cruising altitude (likely 9000).
Would Toronto terminal allow such IFR transit, or would they route me
around it?

Thanks!