If you have your last pay stub, H&R Block will "rapid file" for you the last week of December I believe. It costs more than it's worth to go that way though...it's basically a loan and they charge you EXTREME interest on it. Otherwise the date is January 15 if you're filing yourself. You can file prior to that but the IRS won't issue refunds until after the 15th. Filing early means less wait time and e-filing means your refund arrives quicker. Early, you'll generally get a refund within a week. State refund is dependent on what state you are in. Some within a week and some (California) may take weeks and even months.
If you are in Canada and you know you have more than the standard deductions you can apply for a reduction at source. You will then be taxed appropriately on each pay period. Otherwise you get your refund whenever CRA feels like it and generally the more you are getting the longer it will take. They Just don't want to part with your money.
You can go to a tax prep place, like hr bloc, as soon as you get your W-2. They'll work up your taxes and offer you a loan based on what they say you'll get back, but them you'll owe them their fee plus interest on the loan