I extended my visitor visa 3 times. I had to have an interview for the 3rd time, but I managed to get visa. It is better to explain why you want to stay that long. Don’t write ”sight seeing”.
My case was before the ”new law”, so I can’t help you much. I have been in Canada for over 5 years with visitor and work visa. I wrote about my boyfriend when I extended visitor visas. The interview was held in Calgary, and the officer asked me tons of questions about our relationship and my financial situation. My boyfriend was with me at the interview, too. We told the officer that we would marry soon. Well, I got the visa. ”Common-law” application should be harder than any other case. Good luck to you.