Thanks Marty 321, I just read that on the Lloyd Edward Jones report.
It also looks like CanMex itself only owns 30% of CanMex holdings, which is the subsidiary doing this deal. The rest is controlled by Lundin. So, investing in CanMex would mean 30% of the 80% deal. Still more than 20%, but not by much.
I think I'll invest thru RRS.