The biggest trouble with that is that a big chunk of the work, scouting, can only be done by the coach. I've done that several times, scouting all canadian players available (and I mean all!). I takes a good week, but I still have spreadsheets from way back.
After the scouting bit, yes a trio of managers will definitely work, discussing game strategies, coming up with training plans and following up with managers... It helps having more than one set of eyes and different game experiences or ways of thinking. But that's not the most time-consuming part of the job. I don't think Canada ever had a "formal" coach team for either NT with clearly assigned roles, but I've been pretty involved in strategies and training discussions with the past 2 U21 coaches, so this teaming up naturally happens even though it's not visible or official