In a professional relationship, “Cordialement” is the way to go (“Salutations” works too)

For friends, “à bientôt” is good, “à plus” (same meaning) is good too and a short way to say “à plus tard”

I’ll talk about French from France since I don’t know about Québec French. It depends a lot on the level of familiarity with the person you’re corresponding with.

A typical formal ending would be:

Je vous prie d’agréer, Madame, l’expression de ma considération distinguée.

Je vous prie d’agréer, Mademoiselle, l’expression de mes salutations distinguées.

Je vous prie d’agréer, Monsieur, l’expression de mes sentiments les meilleurs. (I’d avoid using "sentiments" with someone from the opposite gender as it may come off as flirtatious.)

Specify "Dans l’attente de votre réponse" if you want to indicate that you’re waiting for an answer.

If you’re writing to a superior or someone in a position of authority to you (a judge, a religious figure, an elder in your community) and want to be deferential, you might say:

Je vous prie d’agréer l’expression de mon plus profond respect.

Respectueusement,

In an everyday business setting, a typical phrase would be

Cordialement,

Très cordialement,

Salutations,

You should not use any of the above with friends or family.

In an informal setting, you can use pretty much anything you would say out loud.

À tout à l’heure, À demain, À la semaine prochaine, À bientôt

Bises ("kisses", but you can use this with good friends, not just romantic partners)

Ciao (but don’t try to be too hip either)

In informal emails, it’s also very common to use:

A+ (short for "à plus tard")