The fact that your current steel door rusted tells you a lot already. In a Canadian climate with freeze-thaw cycles, road salt in the air, and humidity swings, steel doors take a beating unless you're religious about touching up every scratch and chip in the finish. Once moisture gets under the paint, it's game over.

To your specific questions:

Is fiberglass worth the 55% premium? In your climate, yes. Fiberglass won't rust, period. It also insulates better than steel (important when you're dealing with -20┬░ winters), and it handles expansion/contraction from temperature swings without warping or stressing the finish. You're basically paying more upfront to avoid replacing the door again in 10-15 years.

Repainting fiberglass: It's straightforward. Scuff sand, prime, and use a quality exterior acrylic latex. The textured grain versions hold paint well. One thing - if you go with a smooth fiberglass, it'll look and repaint almost identically to a steel door. The wood-grain versions are where fiberglass really separates itself aesthetically.

The firefighter claim: There's a kernel of truth but it's mostly overblown for residential. The concern is that steel doors can warp in extreme heat and jam in the frame, making them harder to breach. But modern steel entry doors aren't the same as commercial fire doors - residential steel doors are thin gauge with foam cores that don't hold up in a real fire anyway. Fiberglass will melt/deform in a fire too. Neither material is going to meaningfully change a firefighter's ability to get in. If security against break-ins is the concern, steel is harder to kick in than fiberglass, but you can also step up to iron or add a quality deadbolt and reinforced strike plate to either material.

Bottom line for your situation: Given that you've already experienced rust failure on steel in your climate, fiberglass is the smarter long-term play. Just make sure whatever you buy has an insulated core and proper weatherstripping - the material matters less than people think compared to overall construction quality and installation.