I think you can/should introduce the bottle right away, because otherwise, as with your first son, they might never take it... my son took both breast and bottle in the beginning, but at about 3 weeks stopped taking the bottle altogether, even with my own pumped breast milk, which made it very hard to feed him, as I'd always have to be around, always do night feedings, etc... we tried all kinds of nipples/etc, and he just wouldn't take it. (stubborn little man.)
The only 'bottle' he eventually started drinking from (much later, after we started solids at 6 months onward), was a straw-cup (instead of a sippy cup), with a soft straw that he eventually learned how to suck through. They are sold at Zellers (and possibly elsewhere), for about $8. Really great, although I'm not sure that you could try it with a 3 week old?...