Here's my response to Dave; I thought I'd also post it for the benefit of others:
"Rainy Lake and Lake of the Woods are exceptional cruising areas. Weather and bug-wise, late July and early August are usually the best. Speaking of bugs, make a fetish of plugging every, and I mean every, small entrance to your cabin if you value a good night's sleep.
In late summer and early fall, LOW has horrendous algae blooms which Rainy Lake does not. LOW is at the edge of the prairies and has a huge, shallow, south basin that can really kick up. Except in the eastern section (Whitefish Bay), the landscape is not quite as rugged as on Rainy and there are more deciduous trees rather than conifers. But there are a myriad of channels and islands to explore and the fishing is great. There are lots of boat launch sites and when we went there put in near Baudette, MN.
Before I get to Rainy, you will need proper ID such as a NEXUS Card as both of these lakes span the border with Canada. And the Canadians have also required what is known as a Remote Area Border Crossing Permit (RABC) that can be had by mail in advance. This allows one to cross into Canadian waters without checking in. Eventually, it is our hope that they will recognize the NEXUS card in lieu of this additional clearance, but given how slowly things move, I cannot guarantee they will have done away with the RABC by this summer.
Given that 60% of Rainy is in Canada, we always get cleared and spend most of our time in their waters. We feel it is somewhat less crowded, due to the border crossing hassles and additional fishing license costs, etc., but that is exactly why we like to go there. Rainy is a beautiful, intricate lake full of pine-crowned islands. From the SW corner, near International Falls, it stretches 35 miles north and 40 miles east, with many bays and arms in between. It has been said one cannot see all of it in a lifetime, and I am beginning to believe this is true. We literaly cannot get to all of our favorite places in any one summer. The best place to launch here is at the Voyageurs National Park ramp on Black Bay, east of International Falls. Both LOW and Rainy have excellent paper and GPS charts and you must get what you need and study them like a hawk. Rainy is notorious and it has been said there are only two types of boaters on the lake, those that have hit rocks and those that are going to. I probably fall into both camps. It's not that Rainy is shallow, it's just that things can change in a hurry."