The wind builds in Johnstone throughout the day. Getting into to early helps a lot.
I prefer the "back way" near Campbell River; either the Yucaltas or Surge Narrows / Upper Rapids.
From the Yuclatas I go to Blind Channel. From Blind Channel through Greene Point Rapids, Wellbore Channel SUnderland Channel before reaching Johnstone. I monitor the conditions at Fanny Island and then spend as llittle times a possible in Johnstone by going into Havannah Channel to either Lagoon Cove or Potts Lagoon. Then into Johnstone via Baronet Passage.
You might also consider going into the Broughtons and then taking Queen Charlotte Strait to Hardy.
Some more here
North to the Broughtons