One of the first things to consider is if you want to go up the Inside Passage. We had our trip all planned out doing the Inside Passage at the finish of our trip in 2016, but decided to do it at the beginning. Reservations are needed for the Alaska Marine Highway System and we decided that it would be best to get the reservation part out of the way at the beginning rather than having to be in Skagway on a certain date. Others on here have had no problems getting on the AMHS without booking far in advance like we did. We made a couple side trips because we didn't have to be anywhere on a certain date.
Having said that make reservations for July 1st if in Canada and July4th if in U.S. and any other holiday weekends you will be on the road.
Make sure you give yourself plenty of time. We left May 28 and didn't get home until Sept 28, and could have spent more time out, but the camper was getting a bit of a cramped feel towards the end of the 4 months.
We also toured through Yukon and Northwest Territories, Northern Alberta and British Columbia, as well as traveling through everything from here and back.
Brian