Well, since you asked.. You are right not to get into a shouting match, or make a big dispute about this. The folks who own the property, and pay the bills, get to set the residency rules. Haggis95 probably has the best overall advice.
But you might take a more subtle approach. If there is a local gun store where you have done some research, and like and respect the folks who run it, or have done training at a range that your like, and where you feel comfortable, you might just invite your Dad out to that store or range, just to get some information on what you are into.
What father could resist this - his son saying, "Come on, let me show you what this is all about..." Make it clear that you will respect your folks wishes about no guns in the house, if that is their final word. But suggest that, particularly for your father, he might want to at least become familiar with what you are working towards - ie. getting your restricted PAL, and maybe even doing some competitive shooting.
It's really good to set goals, and pursue a challenging project that takes time and money to complete. Make it clear that you will try to get some part-time employment to fund your first gun purchase, if and when that becomes possible. And set your sites high. I differ from most folks who teach intro shooting skills, since I have always had little interest in .22's. Move on up, as soon as you possibly can, to something serious. Plan to get a .45 auto or a big revolver. A .357 magnum is a *really* good choice, as you can shoot ordinary .38 special, which is cheaper, and has less of a kick, and you can also shoot some .357's, which are a little more challenging. My personal favourite is the .45 auto, despite the cost. Its also really interesting to study and learn the history of firearms, by acquiring antiques and early models of various types.
And TargetNorth has a good idea. You can explain and demonstrate your interest in ultimately getting the restricted PAL, and doing some serious handgun shooting. Along the way, once the discussion goes on for a while, the idea of a basic bolt-action hunting rifle might end up becoming a compromise everyone can live with - particularly if your father gets a little more curious. But of course, I have no knowledge of your situation, right? Maybe your mother would be the one who might ultimately become more interested in the sport, given the proper introduction. Or maybe you invite them both out the range, just so they can see what it is all about. I guess the bottom line is that you have to respect their wishes, but you can also make a genuine offer to introduce them both to something that you care about, that requires education and discipline to master, and that is deeply connected to our history and culture as Canadians. We have been, and are, a northern people, in a land were none of us is really more than a few hundred miles away from frontier wilderness. Each of us should know how to drive in winter, use a rifle, navigate a boat, or operate a VHF radio. Expressed like this, what parent would not want their offspring to develop sensible life skills?
Two more cents, from the snow-covered wilds of Ontario...

- Rus