You can grow anything in a pot if you are prepared to give it all the time and attention it will need. Having said that, any clematis with montana in its name will get huge, heavy and want to spread a vast distance - so any grown in a pot will require a good deal of space, and a pretty vast pot There are better, far smaller ones, more suitable for pot culture than the montana group. We have 3 montana, in the ground, and the space to allow them to grow large, and they have - and lovley they are too, as they are now coming into flower - but not really ideal for pot growth. IMHO.
If you desperately want this one, and must grow it in a pot, then start with a good sized pot and be prepared to go up a size or two each year as it grows until you really cannot get any bigger. I have other clematis in pots 18 - 24 inches wide and up to 30 - 36 inches deep, these will not hold a montana for long I don't think. Of course, someone may tell you differently and that is fine ..... It will not achieve the growth it would like to, and although I can and do grow nealry anything in pots, it would seem quite a challenge, and I am not at all sure how long it could last - whereas montanas in the ground can last for many years.