If they switch from F-35s to some more super hornets instead, they ought to save enough for an extra ship or three

Seriously, Canada isn't into the expeditionary power projection business, so they need a multi-role interceptor far more than they need a single engine front-aspect stealthy strike platform that can't carry half the missiles an F-18 can. An F-18 with helmet mounted display, new AESA radar, IRST, and amraams on all pylons, is a hell of an air defense platform. Not nearly as fast as a slick new-build F-15 with -229s, but when the russkies come over the pole they'll be cleaning off the wings as soon as they get to altitude anyhow, so may as well go for max loadout from the start.
IIRC, a superhornet can carry about 10 AMRAAMS. USAF F-15s didn't come with the outboard missile pylons installed so they're limited to 8, however the latest F-15 offering has new air defense pylon options that will let it carry 12-14 IIRC. Either new-build F-18s or F-15s for the same price as a JSF, the training transition is trivial/nonexistent, and existing supply chains still work.
If you're not invading anyone, don't need JSF. Canada has already pulled out of current NATO/US led ops, seems to be a pretty strong indicator of where their defense needs are.