ndm, you've brought up a number of disparate points, some of which perhaps need clarification -
Canada, like the US, uses 120vac, usually a split-phase off 240vac.
Three-phase is often used in NA commercial establishments; public EVSEs are often driven off two legs of a delta-connected 3-phase system, producing 208vac. Our iMiEV charger works just fine off 208vac.
You mention using block-heater connections: I thought those are all simply 120vac outlets.
We had a discussion on using two 120vac outlets off our split-phase system to produce 240vac. See this post:
http://myimiev.com/forum/viewtopic.php?p=8110#p8110
That post refers back to the Leaf forum which shows a safe circuit diagram to accomplish this:
http://www.mynissanleaf.com/viewtopic.php?f=26&t=4774
There is also a commercial product called
Quick220 for safely accomplishing the same thing.
In any case, using two separate outlets whereby each one is off a different leg of 240vac is certainly a viable way of getting you 240vac to speed up your charging time. Need to emphasize testing each outlet for proper polarity before ever plugging anything into it!
Could you perhaps ensure that you are indeed looking at three-phase and not split-phase and exactly what sort of power outlets you're looking at? Since they're only intended for block heaters, do they have a maximum current-draw associated with each outlet?