Are you kidding me?

[GoddessDigi]

You can actually customize onesies lol.
Zero Edge in the Square One mall has them.

[lekate]

It was $18 on Amazon. OMG what store Bells? I ♥ U!

Most of the malls, Rideau, Bayshore and St. Laurent as far as I know have the customizable shirt things, generally a kiosk somewhere in the mall. There's always Bang On, but I'm under the impression they went up in flames recently and probably not back in business yet... Also, much more expensive, better quality, but don't really need that for a onesie (in terms of the printing, they use American Apparel clothing too, not sure about the kiosks, probably generic cheap shirts...). I think too, so long as you don't put it in the dryer the print will last longer (and keep from cracking).