Don't reapply immediately without seeing your GCMS notes first. They will be a little more detailed. Quickly sending in a new application with minimal changes will only lead to another refusal on your record and make you look desperate. I suggest you wait until you can return to Nigeria to apply again.Can I reapply with just a letter of explanation? Because I don't think I have any more documents to provide. About employment prospects, I was thinking of getting my mum who is a nurse in a prestigious organization to get me letter of intention to employ from there but I think this might seems suspicious to the officer.
As others have said it doesn't really matter that you're "stuck" in Russia; filing any application from outside your home country can count against you as it reduces your ties there. A promise of post-graduation employment will also not be very believable. What level of education did you apply for in Canada? A master's degree would be ideal.