As a Canadian I have a weird mishmash that looks right to me. I'd actually use both center and centre in different contexts. Like, the center of a circle is clearly center, but a rec centre looks better that way! (Notwithstanding the red underline my browser with its own preference is giving me...)
That said, I'll never forgive American English for what it did to Aluminium. The word Aluminium just sparkles and glitters like the metal itself, whereas Aluminum has a distinctly cold sound, like an echo in an empty hall early on a winter's morning.