Prime minus 1 variable vs prime plus 2 fixed is a 300 basis points difference. Many economists think that the next few years will be stable interest rate wise - upward pressure yes, but likely within the 3-4% range.
Yes, there is always a risk that it increases suddenly and more than expected (I doubt we will ever see 20%+ again, but possible). So if you feel very risk averse, or your cash flow is extremely tight, fix. Otherwise stay variable. Car finance is relatively short-term and relatively small amounts.
And you can always save your interest gain. With 3% saving atm you will be "in the money" so to speak for quite some time.
I suppose personal preference plays a big role in decisions like this.