Chemical surface etching is the only method recommended by the paint industry for preparing aluminum for painting.
Pretreat and primer in one,(If I recall correctly):
JASCO PREP & PRIMER
http://www.jasco-help.com/products/prod_mg.htm
(go to metal and galvanizing)
Follow instructions in this products use.
Basic Primers that needs some prep first:
or use etching products from Eastwood
http://www.eastwoodcompany.com/
(do a search for "etching")
In using this ,Sand even with grit as much as 600 for a smooth surface situation.
Clean surface well,now you can use anything that specifically takes away oils and waxes but why not do it right with a product from NAPA called Kleanz Easy,its easier and faster.
!!! Important!!!
Then clean final with tack cloth to take any oil from your hands off of it,because oil is the major enemy here,bare hands or any type oils, from the skin or otherplaces is bad news ( you'll get fisheyes patterns).
Primer it.
Dry 30 minutes(avg)
Paint it,Still no touchy with hands,you'd hate to get a single imprint on it at this time,right? :big grin:
I see your in Canada so try for the product called Kleanz Easy.
http://www.martinsenour-autopaint.com
All this will lead to a --secured-- primer,and smooth pro look surface when painted,you can use some of this with whatever paints or primers you have locally, but try to replicate this .
Doing otherwise your just covering the surface temporarly,later to get chips and flaks,aluminum acts bad towards exposure to oxygen and dirt exposure over time.