I do like the way you think.
I'm not sure as to the reasons behind you wanting to own a Case.
If you are looking to buy a project tractor to first restore and then "show it", then the 155 you know about would be a good choice. They are very simple to work on, parts are easy to find and the Kohler is one of the cheapest engines to rebuild, should it need it. The 155 also has that "older look" to it and people often find that quite appealing.
If you are seeking a "work tractor", then the best choice is a 444 Case, whether it just says Case or it says Case and Ingersoll or just Ingersoll. If you prefer the Desert Sunset/Power Red paint scheme like I do, then find a 444 that was made in 1971, 72, 73, 74, 75 or 76. All of these have the Snap-Fast attachment system for hooking up decks, blades and blowers. A 444 from 1969 or 1970 does not have Snap Fast, so stay away from it because old attachments are hard to find.
The 444 is a far better choice over the 446. You can rebuild the Kohler for a few hundred but the Onan will cost you a grand. You won't notice the 2 hp difference. Granted, the Onan boxer engines are smooth compared to the pumping action of the one-lung Kohlers but to me, that isn't enough to justify the higher cost of ownership. If you intend on clearing snow or working in the garden with ground engagement tools, then the extra 4 inches of ground clearance makes a 400 series a lot handier than any 200 model. And if you want a 3 pt hitch, then going with a 400 makes that a non-issue because the hitch was not designed to go on a 200.
These tractors are plentiful in Pennsylvania and apparently not very expensive according to Classic Motion on MTF because he lives down that way. Sometimes, you can find an excellent deal in one state and then find someone to bring that package north so that it's within a day's drive both ways for you to retrieve it. Halifax is only a bit over six hours to the Maine border town of Houlton....as an example. It does take some planning but it is possible to set up a meeting at a specified location in a town such as Houlton so you can take possession of the equipment and then bring it back across the border. It will be subject to your HST but not to any import duties. Since you are not in a rush, you have plenty of time to make something like this happen.