The footprint would be wider, which would increase the static rollover angle (where a line straight down from the C of G points outside the outer edge of the landing gear), but we're not just talking about friction (ie one surface slipping over another), it's the buildup of water pressure on the 'leading' edge of the float that would provide a pretty big force as soon as you had a few knots sideways happening.
I've done a bit of float work, and letting sideward speed build up isn't good - can damage the floats, and I wouldn't want to push it too much anyway, because I think the risk of rolling it over would be quite real.