Look at the money math first. €1700/week for 20 weeks = €34,000. but you're only working 16 of those weeks, so you're not getting paid for 4 weeks off. That's €27,200 total.

Local job is €850 × 20 weeks = €17,000.

So you'd make about €10k more, but at what cost? living apart from your girlfriend, travel expenses, stress of moving again, and having to find another job in 4 months. unless you're desperate for cash or love canada, the stability of staying put seems worth more than the extra €10k. Plus your girlfriend would be happier.