overflying Canada along east coast of Lake Huron

I'm considering either a VFR or IFR flight (Piper Arrow) from the
Detroit area, overflying Canada along the east coast of Lake Huron
north and back into the US at Mackinac Island. (MCD) My route would
be KARB SVM ZR FRUMP YVV WALAC PINES MCD. This route would take me up
the Bruce Peninsula with a some island hopping then back in the US
around Drummond Island. (DRM) Canadian overflight, no landing in
Canada.

My question is the lowest altitude required to stay in radio
communication along the route. Looking at Low level IFR charts it
seems like you would be fine way up in the 10,000 foot range along
airways, but I wonder how I can figure out off airways. And other
options like position reports if I'm too low for radar but high enough
to stay in communication. (Toronto Center I think) It would be nice
if I could figure on 4,000 or 5,000.

Any ideas, or experience in this are of Canada? Thanks ... akiley