The bottom is painted already? Just prep it well, and clean it really good before paint. Wipe it all really good with acetone and a clean rag. The Prep is really the key. Interlux makes a good quality paint that's readily available in Canada. I painted my whole boat with exterior latex and it is holding up really well. I needed ultra flat paint though, so it was a little harder to find an actual marine grade paint that was ultra flat and available in canada.
Get a good self etching primer to hit the bare metal, or it will just peel off.
S.