I am a current US citizen and have an ongoing prescription for a government-controlled substance that I will continue to need for the rest of my life. My current doctor writes my prescription and I must visit her regularly for checkups. I intend to move to Canada and don't know if I will encounter issues having my medication fulfilled through the healthcare system there. I assume I will need to get a new primary care doctor who will be able to write the prescription for me, but will I need to go through the same tests and meetings that I already did in order to get the diagnoses? Or will I be able to start with a new doctor and transfer my existing records and they will be able to pick it up where my US doctor left off? Does it make a difference that this is a government controlled substance?
Not all substances that are government-controlled in the US are so controlled in Canada (and vice versa), so this may or may not matter.
Book an appointment with a Canadian family doctor/general practitioner. Bring as many of your US doctor's records as you are able (or have your US doctor forward your records to your new Canadian doctor). Bring copies of your existing prescriptions, and arrange for your Canadian doctor to give you new prescriptions. US prescriptions are generally not valid in Canada (the same as Canadian ones tend not to be valid in the US).
Note that any good doctor is going to evaluate your prescriptions and may have some opinions on whether they are the best ones for you, and whether the dosage is correct, which is why your existing doctor's notes and a consultation with you will be useful.
As for whether you'll need new tests, that will be up to your new doctor.
Note that until you qualify for your province or territory's public health insurance, you may need to pay for your doctor visit(s). There is usually a short delay before eligibility begins, and registration is usually required. (It depends on the province or territory.)