One GOOD thing about buying a house backing onto hydro right of ways is that you only have 2 neighbours to deal with, not three. Plus if you have a dog you can put a gate in your back fench and basically have a nice little park for him to play in.
Yeah, there have been studies showing some effect of power lines but there are SO many millions of people living near them that if it was significant, there would be a huge outcry by now.
For that matter, if you're so worried about the magnetic fields, I bet you don't hesitate to put an even larger one right next to your brain do you? If you don't know what I'm talking about, it's a cell phone. There have been studies on those that notice an increase in brain cancer for long time cell users.
I bet if you could get your hands on a meter that showed magnetic fields, and you went through any house or condo, you'd find just as much, or more, magnetic fields than those produced by hi tension wires.
Personally I wouldn't worry about it unless you're planning to spend the rest of your life there (say 50 yrs). If you're thinking that this will be your starter place, and plan on buying another, or a house within the next 10 yrs, I'd say go for it....