Is there any tariffs or taxes once you buy a bike in the U.S importing it into Ontario. For example if buying from E-bay?

Typically no but it does depend on the country of origin and how it is shipped over. If it is shipped as a "gift" then there is no tariff or duty. If it is shipped legit as a sale it now becomes a matter of origin, if it is made in the US or Canada then it is covered under Nafta and there is not duty as long as the paperwork is filled out correctly.

Depends on where the bike is made. If it's american made, then you won't pay duties on it, but you will pay taxes on it. If not made in the USA, you will pay both duties and taxes.

Declaring it as gift doesn't mean you won't get charged tax. I don't know where you got that from. If you're shipping it, you get an exemption of $60 CAD if it's a gift, but that can be annuled if it's determined not to be a gift and you can get in trouble for that. A bike isn't something you should be under evaluating at also......

If you bring it back personally, well you get the exemption of merchandise of $200 after 48 hours or $750 after 7 days.

A word of caution though, if you use UPS or private courriers, they can charge brokerage fees, which people confuse with customs duties and taxes. Brokerage fees is basically a fee to UPS or courrier for them to bring it through customs for you and they tend to charge outrageous amounts, and is not related to your customs duties and taxes responsibilities.

Hope that helps.

Talking to UPS the other day and they were telling me that you can have the package arrive at the terminal and agree to do the paper work yourself saving a substantial portion of the brokerage fee.

I have purchased three bikes from the states and all of the transactions saved me considerable money. the ideal situation is to have it shipped USPS instead of a courier.
They don't gouge you for brokerage fees like UPS and FED EX. The tax and duty ends up being what you would have paid in Canadian taxes anyway(GST ,PST)

Wow didn't realize the USPS would ship a bike box. Where did you pick it up and how much was postage?

Wait a second lets take a logical look at this. An Ellsworth Truth from Beyond bikes is $1995. Using the best US-CND exchange rate you are looking at $2368. Now no matter what payment method you use you are not going to get this exchange rate it is always going to be a couple of points higher. If you then add on at least $50 for shipping charges without even factoring in the difference in exchange rates you are looking at $2411. The Canadian retail price is $2499.99, sorry but I fail to see the significant savings here.
Now if we look at a frame that is not covered under NAFTA and will be subject to duty lets see what we get. A Look 585 frameset from Competitive cyclist is $3000, the exchange rate puts this at $3531CND plus shipping and duty. If memory serves me correctly the duty is in the range of 20% so this now puts the price at $4237. This frame set retails for $4299 CND. Sorry but I am still not seeing the savings here. Either one of those bikes could be had for a better deal from you're LBS. As a matter of fact a quick search shows you can find a Look 585 frame for $3699 CND.