How many interstates continue as freeways on the Canadian side anyway?
Technically only one that has zero at grades on either side (ON 405 > I-190).
There are several that sort of count; the Peace Bridge (NY-ON) is actually a freeway only on the Canadian side, while the Thousand Islands (NY) and Peace Arch (WA) are at least free flowing if not freeway by definition.
I don't see any at-grades on ON 402. I'd count the Peace Bridge as freeway-freeway now that the at-grade on the NY side has been removed, even though the bridge would still be a super-2.
Going down the whole border:
-I-5/BC 99 has an at-grade intersection north of the border and crosswalks in the park
-I-15 becomes an at-grade expressway
-I-29 becomes an at-grade expressway
-I-75 just ends
-I-94/ON 402 - see above, no at-grades detected
-Ambassador Bridge - direct freeway interchange on US side, surface street in CA
-ON 401 - will be freeway/freeway when the bridge is completed
-Peace Bridge/QEW - see above, freeway in CA, direct freeway interchange in NY
-I-190/ON 405 - see above, freeway/freeway
-I-81/ON 137 - surface street in CA before becoming a freeway and connecting to ON 401; super-2 bridges on either side
-I-87/A-15 - at-grade with stop sign on CA side
-I-89 - becomes (brief) four lane expressway, not 100% sure if it will be free of at-grades if/when A-35 is completed
-I-91/A-55 - at-grade with traffic light on CA side, second at-grade 5km from the border
-US 201/QC 173 - would become the reverse of the typical situation if A-73 were to be completed (not likely)
-I-95/NB 95 - at-grade on CA side
-NB 1 - freeway on CA side, ends on US side - could become freeway/freeway if Maine were to actually build the east-west Turnpike they keep talking about
This is all light-years better than the situation on the border when Mexico, which has nothing even remotely resembling a freeway-freeway crossing, at least for cars; trucks have the World Trade Bridge.