Unless you had some way to contact each other from a distance, I would say paddle and portage together.  Too many possibilities of one or more canoes straying off path, getting lost, taking wrong portage, having a hold-up for whatever reason, capsizing, unable/fearful of crossing a windy section of water, etc. etc.
On one trip I was on, 2 solo paddlers and a tandem in a canoe; the canoe was substantially faster and finally just pushed on ahead to a designated camping lake.  Left a message for us to "catch up" at a portage....we were ready to stop 2 portages before we knew they were planning to and it was supper time, so finally we did stop without them.  We were annoyed and they, when we didn't show up, were both worried and annoyed....an uncomfortable end to an otherwise pleasant group trip.  :thumbdown