Take measures to copyright your script before sending it out. Copyright law differs from country to country. In general though, you can not copyright an idea only the actual execution of that idea; ie. the work. To my (non-lawyer) understanding, the mere act of creating a work brings with it the de facto copyright of that work. For legal purposes however, you want to make that copyright official.
In the US, you can register your script online at the US Copyright Office for $35 (even if you’re a foreigner). In Canada you can register online at the Canadian Intellectual Property Office – the cost is $50.
In the US, you’re asked to upload your script. Makes sense. In Canada you are not able to do so. You can’t even send it in by mail. They don’t want it. Have no place to file it. All they ask for is the title and your $50. How does this make any sense whatsoever? It doesn’t. It’s a cash grab. Other than being a record that on this day in history you copyrighted something (we’ll take you at your word) called “TITLE”, it’s a stunningly embarrassing system. That said, an entertainment attorney will tell you that as a record of something it’s better than nothing. Your call.
Speaking of being on the record. It’s important to note both the US and Canadian offices will publish your personal information on the internet right down to your address, email and phone number. Publicly and forever. So if you’re a fan of privacy and / or write things that could get you a fatwā, there is another option:
The Writer’s Guild of America West has a private online script registration service for non-members. Cost’s $20, does require you upload the work but it only lasts 5 years. That’s more time than you need before your script is queried out anyway. This doesn’t make it official in the eyes of the law the way the gov registrations do but remember, creating the work comes with it an implicit copyright anyway. All you’re trying to do beyond that is securing legal proof.
And as far as legal proof goes there’s nothing black and white about legal claims. You rarely hear of copyright cases going to trial. Most are settled out of court. I still have a drawer full of print-outs in sealed postmarked envelopes. The ultimate paranoid fail safe. Fact is, the more sources that prove you created this work before X date the safer you are.