Part of the problem that arises with carrying on a bike comes with needing to decide which hand you're going to draw with,
IF
you are even inclined to draw the gun while on the bike.
If you think you might have a reason to draw the gun while riding, you'd have to draw left-handed but you'd have to holster it before coming to a stop in most, but not all, cases.
If you're going to be sitting at a stop light, you'll need to draw right-handed and you'd have to reholster before proceeding again.
In all cases, can it be done quickly? Carrying two handguns doesn't even solve all of the problems.
Guns and bikes are necessarily a good combination, in my opinion.
I carry in a tank bag (rarely) or a fanny pack (mostly) with the assumption that I'm never going to attempt to draw the gun while riding.
--Wag--