Rachael, so although you have known him for nearly 4 years you haven`t seen too much of him. He`s either been living in Wales or in the army. He may be a lovely bloke but he has not shown much staying power.
I would seriously advise caution. You are both young and, whether you want to believe it or not, the likelihood of the two of you staying together forever is very little.
No matter what you may hear, this is still a pretty good country to live in.
You have a family in Newcastle and I`m sure you have already made friends in Wales. Why not let your boyfriend go to Canada (if the job transpires) and let him work there for a period, say, 6 months.
Then the situation will be much clearer. If he is in a stable job and you both still want to be together then you can decide to go and join him.
You`re still young, lovely girl, and you should think before you leap.