+1 on the rain gear. Expect and prepare for bad weather. I have been up twice and departed mid June both times. The first time, it was cold and rained from MT to Anchorage, but was mostly nice the rest of the trip. Last summer, it rained from Banff to Whitehorse, with a terrible hail-thunderstorm around Summit Lake, but little after that.
Expect +-40 at night, so heated grips, electric jacket liner, hand guards, and bigger windshield sure help. Suggest a Pinlock shield if you don't have one. Didn't fog up, even in the mid 30's.
I met a Harley rider at Pink Mountain gas stop last summer, 200 miles up the Alcan, on his way home to WI. It was pouring and he was totally disgusted with the trip. He had started June lst and said he had a rain cloud over him for the total trip. Also hated the roads. The locals around Anchorage indicated the summer of 2008 never arrived. It was a cool, crappy, cloudy summer.
Never had a problem with bugs, camped, and didn't even have bug spray along last summer. Not sure about the reports? Maybe the bugs arrive later in the summer.
I picked up $200 Canadian from my bank before leaving. Call your credit cards letting them know you will be out of the country. Unlike the US, pay phones are available. I purchased a Canadian calling card at a campground, which was inexpensive. Once on the Alcan, don't expect cell service.
Purchase a 2010 Milepost, which should now be available. Route suggestion. First time, I rode the Alcan both ways. Last summer, rode back to Watson Lake, then took the Cassiar south to Hyder. Except for construction, it is now fully paved and a wonderful ride. I don't mind riding road construction, but have little interest in riding roads like the haul road, so I can't help with that. I like the southern part of AK better, so this time I stayed around the mountains at Valdez, Seward, +Anchorage. Skagway is beautiful, but a tourist trap.
Enjoy. JR