Plan for the portages - the canoeing takes care of itself.

Even though your mileage may be 95% paddling, portaging is the "half"
of the trip that takes the most planning.

Decide ahead of time if you are going to single trip (i.e. everything over on one pass) or double trip (carry "half" the gear over in each of two trips) - then think about how many loads you will have, and then pack the gear accordingly.  If you can't reasonably double trip, then it means doing 3 loads/trips across - if that's what it takes, that's what it takes, but I'd try to avoid that.

e.g. - A canoe is one load, usually with a spare paddle and maybe the fishing poles tied in under the thwarts, and maybe with the PFDs fastened around the seats or thwarts;  with 4 people, the food  pack is going to be another big heavy load; so that is the first trip over if you are double tripping, and the guy carrying the food pack will likely be hand carrying two paddles unless you have an easy/quick way to secure them both in the canoe.  If the canoe is a lightweight kevlar model, the guy carrying the canoe can usually also carry a small to medium not too heavy pack - try to average out the loads each person will be carrying for each trip, unless one of you is "petite" and needs to carry a lighter load. (You don't normally want a 90lb weakling carrying the 100lb food pack! - aside from not being "fair", a too heavy load can lead to injury or early burnout. - the second trip would be everything that is left, which would normally mean at least one large pack and a daypack? or two large packs? or some combination - think ahead of time how you want to carry what's left.  Avoid having a lot of loose items - one daypack per canoe should be sufficient to carry for two people, raingear, lunch, fishing gear, water bottles, suscreen - what you want easy access to during the day - before you start over the trail, put all the loose stuff into that daypack.  If you have a lot of loose stuff to hand carry, more likely than not you will wind up leaving something behind at a portage.

You can alternate the loads between you, so that you carry the canoe on this portage, and your buddy carries it on that portage; or you can keep the loads constant - i.e. you always take load A, which has this and this and that.  

Keeping the pieces of a given load the same each time you portage is more important than not. i.e.  Load A always = the big green pack, the tackle box, and two paddles - no matter who is taking Load A, it is always the same load;  whoever is taking the canoe is also carrying the daypack, etc. - saves time at the portage if everyone knows what to grab without having to discuss or think about it.  That also helps to avoid leaving stuff behind because you thought the other guy was bringing the extra paddle or the tackle box while he thought you were bringing it.

Some people plan the packing so that each person is carrying thier own personal pack over the portages (as well as thier share of group gear) - this helps eliminate overpacking by some people - I wouldn't mind at all packing a 100 lb pack with luxury items if I though you'd be carrying it for me.