This and Google Earth, http://www.gisapplication.lrc.gov.on.ca/CLUPA/Index.html?site=CLUPA&viewer=CLUPA&locale=en-US
Use Google earth to find an open area, and the land use atlas to see if it's Crown Land. If you find a good spot, be stingy with it, and keep it clean. Avoid anything that looks like it's used by ATV's for obvious reasons. Should be plenty of open spots Bogs, Power Lines, etc.
Little late to the party here, but I contacted the PoCo in MB to ask about shooting on their right of ways, my email got bounced to a couple different people before someone more senior received it, they said that they completed understood wanting to use the right of ways for LR shooting, but said even though it's a crown corporation, it technically isn't crown land, they were also a little against the idea due to the potential to damage equipment, as well as there being a chance of crews out doing maintenance.
tl;dr - Email the power company and ask first in my opinion.
If you can hunt there you can shoot there. I don't know about Manitoba, but in Ontario Hydro One doesn't own the right of way, and as long as you're not endangering one of their employee's, or equipment I highly doubt the Crews on the ground would give a crap.
I wouldn't ask them ####, it's not their land, and they probably don't get to decide how the land is used beyond effecting their operations. If it's safe I'd just go shoot, esp. if it's an isolated spot.