The only reason I'd go with the Gripen as a 2nd fighter would be to partner with Saab on their Next Generation fighter (building an initial batch of Gripen's here would get our workforce trained for the new fighters). There is an expectation that their Gripen replacement will be larger and have longer range due to the fact that since joining NATO their front line is much further away.
Sweden will however need partners to get their program off the ground due to the cost of such a program and they are the only realistic partner for Canada that would give us the option of domestic production and integration of Pratt & Whitney engines in the design. You're not going to get that from Dassault, GCAP, FCAS or NGAD. If domestic production is a key objective then partnering with Sweden is likely our best option.
If we forget about the idea of domestic production or integration of Canadian engines then the program I'd pick to join is GCAS. The design is further along than the others, the UK is most likely of all nations to remain a firm ally of Canada (and Italy and Japan less likely than France or Germany to have any significant political differences with us) so probably the more stable alliance. Also, the design is focusing on extended range as both the UK and Japan have very large airspaces to patrol which would be a major requirement for Canada as well obviously. The problem though with the program is that as advanced as it is there is likely limited opportunity for Canadian industrial participation in the program.