Veeman, I would suggest you declare it. The tax, if any, will be trivial. Probably 5% or less.
The expensive thing is to take things across in the other direction - from the USA to Canada.
Going in that direction, the customs agents will hit you with 7% provincial tax, plus 7% federal tax (GST), and, if you can't prove the goods were made in either the US, Canada or Mexico (the NAFTA states), then you get hit with a further 9% duty charge.
So taking a german engine from USA to canada = cost plus 24% taxes (not counting brokerage fees if you have it shipped).
Taking a german engine from Canada to USA = (I would guess) cost plus 5% taxes or less...
And 935 Racer - better rethink that tactic. I took a used water-cooled intercooler across the border last year, and being a good boy, declared full price value. Even so, I was ushered into the search area, where they informed me that everyone importing auto parts into Canada that week was being given the fine-toothed comb search, as they were well aware that Canadians habitually under-declare the value of auto parts. They spent about an hour fiddling on their computers - I couldn't see the screen, but I suspect they were surfing Ebay. They were just salivating to catch me. Too bad for them that I was honest! They eventually just got bored and sent me on my way, after about an hour of cooling my heels.
Canadian customs agents are getting meaner every year, demanding 40% pay raises and guns, and they've pulled a bunch of wildcat strikes, closing down borders and even Dorval international airport last year. Your tax dollars in action (or maybe not yours exactly, if you habitually under-declare!).