I spend over 100 days a summer paddling west coast Van Isle.
I completed the Port Hardy to Tofino Section late June - Early July this year (2009). This section is the most problamatic for weather and waves, therefore its best to plan it during good weather. Mid summer is fine, as long as you are comfortable with FOG, and are willing to get up early, paddle early, and get off the water early. Our typical day, was awake at 4am (listen to 0400 weather forcast), pack up, and be paddling by 5am (watching the sun come over the mountains). In this way, we were able to get a solid day of paddling in before the winds picked up (start around 1000... peaking around 1400-1500).
The section from Tofino to Victoria should not be under-appreciated in its difficulty. Long sections of exposed coast with few pull-outs.
Once through the Juan de Fuca straight, after completing the entire west coast, the paddle back up to Hardy would be childs play in comparison. Do not underestimate the wind waves that can build up in the Salish Sea (Georgia St), or the tidal rapids which occure in the norhern Gulf Islands (quadra etc) and Johnstone St. I, personally, once watched a pair of kayakers launch into the Johnstone St, and half hour later, one was dead.
Most commercial companies do not operate multi-day trips after September. One- the summer tourist season is mostly over. Two - the weather becomes tempermental, with the first real storms of the Fall arriving around Canadian Thanksgiving. Three - people generally dont like to paddle the whole trip in the rain.