So far as I can determine there is no evidence that is true. He was calling for a peaceful referendum on Sikh independence, and it seems that the government of India had him murdered for that.
We can tell Justin Trudeau "I hear you" and say nothing to India. This is not our problem.
There has been no evidence provided that India was involved in any way.
I find it hard to believe that India would assassinate Najjar, when there are far more dangerous folks to India out there