The realms from Strategic to tactical are all intertwined, and need to be aligned properly in order to function. The CF exists to protect Canada and Canadians (Strategic), thus it also protects me and mine (Tactical). You should also re read my comment, I also included all Canadians as the people I protect first and foremost.
As Tango2Bravo said, this does not preventing us from helping others, indeed there may be occasions where helping others is indeed the best way to support the national interest. As Zipperhead Cop pointed out; a horde of trained rats might also prove to be the most effective means of solving a problem (although I can't imagine what that problem would be..... ???). The government chooses the tools to solve the problem, we in the CF are tools to meet a broad range of potential problems and deal with threats to Canada and Canadians.
Just like your own toolbox in the garage or in your closet, various tools are designed to do particular things. You can extend their uses a bit, like using a screwdriver to pry something open, but it is neither safe nor desirable to do so for a prolonged period. "We are the Canadian Forces, and our job is to be able to kill people." isn't rhetoric, it is fact. We can undertake limited humanitarian aid and reconstruction, and will do so when it supports the CF mission on the ground. If you are looking at bigger scales of aid or reconstruction, there are other appropriate organizations which concentrate on these issues (and occasionally hire private contractors for security if they are unwilling to deal with military forces).
Your desire to do development and aid is great, and I encourage you to do so, but please ensure you understand the strengths and limitations of organizations to deliver aid and development and choose accordingly. If you join the CF only to do humanitarian work, you may find it frustrating. If you want to be a humanitarian first responder, the CF is one avenue to approach, many NGO's do this sort of work as well, but are not self contained like a military formation. Long term aid and development can be conducted by NGO's and government agencies, if that is what you want to do, then a short career in the CF might be a good stepping stone to reach those goals.
Bon Chance!