Do I have “right of abode” in Britain if I was born in Canada in 1977?

No, Canada has been a separate country for a long time

No, and no. Canada became an independent country in 1867, but, we are still a Commonwealth one.

No such thing as "right of abode." Nor "commonwealth citizenship." IF one of your parents was a UK-born UK citizen at the time of your birth, and you can prove it, you may have UK citizenship by descent. You cannot pass on such citizenship to your children. Citizenship by descent is only good for one generation.

Ancestral visa based on grandparent's UK citizenship had to be applied for before you turned 30, so no chance of that now, even if you might have had any sort of claim for that years ago.

If your parent/sare British citizens then you are a British citizen by descent and can prove that via written records you can apply for a passport and so will have right of abode or if your grandparent/s were/ are British citizens then you could apply for an ancestry visa which enables you to live/work in the UK for 5 yrs, at the 5 year mark you can apply for ILR and 12 months later citizenship so than you would have right of abode...... there is no 'commonwealth citizenship' which enables you to just apply for and get a British passport.....

There is no 'commonwealth citizenship'. Unless you have a parent who was British at the time of your birth, you are only Canadian. If you have a British grandparent and are willing to work, you can apply for a five year Ancestral visa.