Hi! I hope you don't mind if I will be the one to answer.
Canada route:
during breaks always choose the place where canada is in. If canada is nowhere to be found, you can just skip break by going to class. And don't forget that you can select floors.
(You can also give gifts! Like soda (it doesn't matter which one, as far as i know), etc. You will see a yellow thingy next to backpack when you are able to do so. Although I will tell you when you can do it anyway)
Fail English test. To do so, always choose the third option. If you did everything right, canada will have to tutor you.
During tutoring ask "Are you and Britain family?" (During this event you can give gift. But you wont be able to buy it beforehand. BUT you will be able to get it if you visit one of the clubs during prologue (VISIT, not JOIN))
During Math project choose Finland, Italy, Canada. Then choose these options:
"We should listen to what Canada has to say"
"I think Canada's is really nice"
During break, in Schoolyard, choose "Follow Canada". Then choose:
"I will help you through this"
"Trust me, I will help as much as i can"
On Tuesday meet with Russia or America during break and agree to help them to find Canada. I recommend Russia tho. You will see why.
On question "Where could he be?" choose the third option.
If you choose to go with Russia, you can say "I love you. You're important and deserve the best things in the world" when you finally find Canada.
During break, in Club hallway (if Canada is there ofc), choose "It's a great idea" and then "Sure".
When you have a choice to write a love letter, do it. Write it for Canada. Context of the letter doesn't matter.
That's all. Other choices don't matter. It also doesn't matter if you study or fall asleep during class. I recommend the 2 option tho, just so you won't waste your energy.
Russia route:
Pretty much as Canada's. Don't forget to spend time with him on breaks and give him gifts, if you want to ofc.
During the first break choose "Talk to Russia", then "Stay with Russia" (You can give gift during this dialoge)
Pass the test. Always choose the first option, in other words. If you did everything correct, Russia will ask to help him with English. Obviously, you should agree.
When you are in his house ask:
"You like ballet?"
"True, his music was amazing"
"I love Tchaikovsky"
During Math project, join America, Russia and Ukraine. Then choose:
"Shut the f*ck up, both of you"
"Stop fighting, you f*cking idiots"
"Let's use red"
"No, let's keep red"
"I actually remember some stuff about him"
"I think he's famous for the law of hydrostatics"
"Yes"
During Tuesday meet with Russia and help him to find Canada. On question "Where could he be?" choose the third option.
On the next day, during the first break, choose "Not even the most annoying people would like him"
On the next break choose to stay with Russia. Then "I was looking for you" (You can give gift here)
On the next day, during break in Club hallway, choose "Pass it to Russia"
Then just spend time with him during breaks. There won't be any choices there.
Then choose to write a love letter to Russia. Context doesn't really matter once again.
That's all! If you have any questions about other routes (including side routes like Spain, Japan, Italy etc) you can always ask! If I didn't mention some choices, then they don't matter. Do whatever you want. Although, I can't also be sure that everything I DID mention affect anything as well. I just told what I did to get those endings.