Running away from home requires an explanation

No, it doesn't. You're a legal adult: when you move out, your parents can only make you feel bad about it; they can't force you to explain, or to return. Your home is, as of the day you turned 18, where you say it is.

My mom gave me a death threat saying that if I ever leave the faith then I'll get killed.

If you believe she's sincere, report this to the police. It'll create a paper trail, which will be useful if you end up needing a protective order later.

I'll go through a lot of physical abuse

If your parents lay a hand on you without your consent, call 911. Your parents' very limited privileges to physically discipline you ended when you became an adult; now that you're an adult, it's plain old assault, and domestic abuse.

I would end up getting an arranged marriage

In Canada, the only person who can consent to your marriage is you. Nothing your parents can do can legally compel you to marry someone else.

I'm obviously in no position to tell you how to live your life, but in your shoes, I would strongly consider keeping your beliefs to yourself while you move out, and then - perhaps, when you're ready and secure in your new life - maybe telling your parents about your choices in your faith. You'll discover, once you no longer live under their roof, that their power over you is a lot less than it seems right now, and you'd still have the option of going no-contact if things went badly.

Disappearing is not illegal, but your parents will likely report you missing. When - not if - the police find you, they will respect your desire to be left alone, since you're an adult and not obviously a danger to yourself, but they will almost certainly tell your parents that you're alive and okay. Leaving a fake suicide note is a tremendously bad idea, for a bunch of reasons, not least that if you're convincing enough for long enough, your parents might have a basis for reporting you as dead, which will fuck up your bank accounts, your job, and your credit cards for a good long time, and be a tremendous problem to sort out once it happens.

Ontario also has a plethora of domestic abuse programs you can use to get away from this and to protect yourself:

• Legal Aid Ontario's Domestic Violence section will get you a two-hour free consultation with a lawyer, if you need one (for example, to help you navigate the restraining order process, or to determine whether to file a police report)
• Distress & Crisis Ontario runs some crisis lines you can call if you need advice, or a friendly voice
• Canadian Mental Health Association has a number of services, ranging from immediate crisis assistance to help finding a counsellor to help you work through the psychological side of your situation

Whether you're planning on moving out politely or abruptly, it pays to do some prep, first.

Before you move out, gather the following important documents:

• Your passport (if lost, apply for a replacement through Service Canada)
• Your SIN number or card (if lost, apply for a replacement through Service Canada)
• Your driver's license or Ontario ID (Service Ontario)
• Your OHIP card (Service Ontario)
• Your birth certificate (Service Ontario)
• Your bank cards and credit cards (if lost, go to the issuing bank in person to access your accounts)
• Your T4s and last year's tax records (you can get replacements through CRA, but it's a pain)

In addition, prioritize what you're bringing with you. In extremis, you may need to leave with what you can carry on your person, so prioritize things that are both useful and portable. Laptops good, furniture less important - you can always find cheap temporary furniture on Craigslist or Freecycle, or a Value Village. Leave your books, except for one or two sentimental favourites.

Finally, know where you're going, even if it's to a domestic abuse shelter.

The day you move out, bring all of those documents with you and keep them on your person until you're sure you're safe. Immediately:

• Empty and close any bank accounts your parents may have had access to. Open a new chequing account at a bank your parents don't regularly use. Keep enough cash to make it through the week.
• If you're staying somewhere shared, consider getting a safety deposit box at your new bank. They're about $60/yr, which is way less than the cost and headache of replacing your documents.
• Pay off and close any credit cards in your name that your parents may have had access to. Apply for a new card through your new bank.
• Pay off and close your phone plan, and get a new phone plan with a different carrier or brand (if they're on Telus, get a Koodo phone, for example). Give someone you trust your new number.
• Remove your family from any emergency contact information at your doctor, your college, and so on. (Consider getting a new doctor; it's not as urgent, as Canadian medical licensing requirements should stop your doctor from sharing your medical info with your parents without your consent.)
• Close your social media accounts. If you must post to Facebook, (a) open a new account, and (b) vet your privacy settings very carefully. I would recommend not doing so until you've figured out how your family has reacted and whether you need a protective order or not.

Using a different vendor acts as a safety net by stopping some well-meaning customer service rep from "fixing" your account if your parents play the 'we used to share it, I don't know what happened' game.

You can do this. Many 20 year olds move out every year. It's scary as shit, but you're not alone.