> massive hydro energy resources

That is irrelevant unless Norway has unused capacity.

If a country adds electric cars using more electric power, then what really matters is how that extra power is generated.

It gets weird in Europe because adding extra load in Norway could easily mean that Poland does more generation using coal.

I'm in New Zealand where the government owned generators are preventing solar installations. One example was via an unobvious regulation that the installation had to handle massively overengineered earthquake rules. Meanwhile we use coal or imported gas when the isn't enough rain for our hydro. And we waste about 10% of our total capacity exporting (via one aluminium plant).

Going all electric with cars would add ~10-15% of electric demand. That's a bit, but not really a deal breaker, and something Norway would easily be able to offset by adding more wind turbines.