If you're using it for low hours, year round, consider either a 10w-30 HDEO dino, or a 5w-40 HDEO synthetic.
If you accumulate enough hours to warrant multiple OCIs/year, then perhaps a 15w-40 dino in summer, and something thinner for winter.
The reality is that most small diesel utility tractors from major reputable brands don't need special attention. About the only way to kill a Kubie or a Yanmar is to run them completely out of oil. If you only knew how equipment is treated in third-world countries, you'd not worry about your actions quite as much.
You have some good Canadian brands to choose from up there; should not be a problem for you to locate one.
I run the AMSOIL 15W40 Heavy Duty Diesel and Marine (AME) oil in my L4300 Kubota. Mine sees reduced hours during the winter months so I'm counting on the marine additives in the oil to control moisture when it's not in use.
The dealer recommends 15W40 Rotella.
I have a 2004 kubota rtv-900r and i was using m1 0w-40 and fram motorcycle oil filter. I ran that for 250 hours and changed the filter at 125 hours. now i am running m1 5w-40 tdt at 22 dollars a qallon and a the same filter. same oci's are used.
If memory serves, a WIX 51365/NAPA 1365, or a pile of others will work.
Check Fram's site here and here for starters. Cick on the filter number, then go down to the "competitors" list for a pile of alternatives.
I use Delo 15w-40 with 25 % 15w-50 synthetic mixed in in my Kubotas. However, I make hay which is very dusty so I do much more frequent oil changes. Without that, I would go with the Shell Rotella T 5w-40, which I have used before but decided against it with the frequent oil changes.
I use Wix filters. Carquest, Baxter, Napa, etc. ought to be able to match the correct filter for your tractor. Or, go to the Wix website and they have a filter finder guide. Just enter Kubota and then find your tractor model. Cost is about half of that for a Kubota OEM filter. I would not consider a Fram even if it was free. I use the Napa Gold or equivalent for the tractors, although I think silver is good enough for cars.
I started using the CI-4plus 5w40 Rotella when I first started running Kubotas on our farm. After 1-1/2years of oil testing, they get nothing but Schaeffer oils though I must say that there are other oils that will run the same intervals. The problem was that in my case all of them costed more. Truthfully, your Kubota will run way longer than you want it to on about any oil that's up to their specs. It's only when you are trying to extend intervals as long as you possibly can that you need to pay attention to what you are using and paying for.