I think you worry too much. If you fear the scenario you describe you should never, ever, get on a plane. Take a ship but then, they could be lying too couldn't they? If I were you and you can't afford your own plane or seagoing vessel I would stay right where I am.

LOL!
You'll be fine!
The plane is loaded with enough fuel to only get to Spain, with a small amount of surpluss — this way they can load more pay-cargo in addition to people and their personal luggage.

Sometimes planes are diverted for problems, such as weather or mechanical problems, but the airports diverted to are very very close over their intended flight pattern. So, if flying from Canada to Spain, they may land in New York, USA or somewhere in Portugal in the case of emergency.

They simply wouldn't have enough fuel to go off flight from Spain to Pakistan, Mongolia, or Peru. …hmmm.. Unless someone hijacked the plane immediately and flew to that alternate destination that is of equivalent or lesser distance. Changes of that are almost nil.

As for most things in life, you can never be 100% sure. But you can evaluate the probability. The only times I know about when a plane is not flying to the announced destination involves hijackers.

When was the latest hijacking? Well of course 9/11. So a few planes every 10 years or so. Lets say 5 planes every 10 year = 0.5 planes/year.

This is then divided by the total number of commercial flights for a year. This is roughly 800000 per month in Europe and probably as much or more in the US. This gives 1.6 million/month or 19.2 million/year.

And of course the world isn't only Europe and the US, so lets add a few million more for the rest of the world and make it 25 million flights/year.

The actual number is probably much higher.

0.5 / 25 000 000 = 0.00000002, or 0.000002%

Then you will have to judge if this probability is good enough

Interesting question.

Don't trust them… Don't fly.
Drive by yourself…. Take GPS with you…