best to have the letter, whatever your marital status. They usually ask abouyt the other parent, to any adult traveling alone with kids.

DON'T forge a note though, because unless it is serioucly notarized and all that, it won't satisfy them if they're actively suspicious...and the next step is to phone the other party. So don't make an annoyance into something worse...

Willie-O,
blended family, one part Canuck, one part Murican.