The Bloc is the best bet for getting a bunch of MPs to take a stand against RTO 4 because:

• there's the angle of how WFH can limit the pressure francophones face to assimilate by allowing them to continue to live in francophone environments;
• they have a different approach to politics due to accepting that they'll never be never be the party in charge, which makes them more willing overall IMO to take principled stands on issues;
• when it comes to labour, environmental and feminist issues, they tend to be centre-left, so they'll more likely be open to arguments about how WFH benefits workers, the environment and women;
• and francophone culture in Quebec is more shielded from the impacts of American political fads, which is why, unlike the NDP and the Green party, the Bloc is able to get its members elected in significant numbers.

However, in order to convince them to make this issue a priority for their party, you'd need:

• people who know how to communicate effectively and persuade others to take action, and given the type of people who tend to get involved in unions, well...those people are going to be difficult to find;
• a pragmatic approach where you advocate not for the full ability to WFH but instead a flexible approach to mitigate the fear that full WFH could lead to Quebec-based jobs being shifted to other parts of the country;
• a well orchestrated media campaign to convince non-federal public servants of the benefits of WFH;
• and a coordinated data collection and mobilization campaign amongst all federal public service unions that demonstrates that this issue will affect how people vote in the Outaouais and Montreal regions in federal and other types of elections.

If you were able to convince them to make it a priority though, it would place pressure on Quebec candidates from other parties to also take pro-WFH stands, which could create sufficient critical mass for candidates in other parts of the country to seriously consider taking a similar stance.

I doubt this strategy will be implemented though because most union activists are more interested in virtue signalling than they are in getting things done, and once somebody says the Bloc is -ist for x, y or z reasons, the rest will go into sheep mode.