I doubt if Haig-Brown, himself, was directly involved in the stocking of Atlantic salmon in Vancouver Island rivers. He was, after all, not a wealthy man (he was a writer fer chrissake) and any such undertaking would have been almost impossible for a private individual in those days. The only reference that I can find in that regard is from The Western Angler -

"Annual plantings were made in the Cowichan, and occasional plantings in other Vancouver Island streams, for a sufficient number of years to give the experiment a good chance of success, but there have not been more than two or three properly authenticated returns."
The Western Angler - 1939

He did, at least at that time, feel that the establishment of Atlantic salmon in BC waters was a good idea and that it would probably not have a detrimental effect on native species. But that was then and this is now. I can't see how anyone could look at the disastrous consequences of salmon farming in Scotland and Norway in terms of pollution and disease without being extremely concerned about the galloping growth of salmon farming in the Northwest.