If someone registered a lawsuit against me for money he lent five years ago, if I am never served, how long until the suit expires? The suit was registered in Ontario where I lived at the time. I now live in BC.

The suit doesn't expire. The Statute of Limitations refers to the time they have to INITIATE legal actions. So once the suit was filed, the SOL no longer applied.

If you weren't served how do you know the suit was filed? Maybe a judgement has been entered against you.