I rather suspected that they cooperated with each other. After all, we haven’t been at war since 1812. However, are you saying that they use the same facilities? I’m pretty sure that isn’t right – at least not at this time. Maybe at some time in the past that was true.
Also, this doesn’t really answer the question of why the coins are so similar. Was somebody just being lazy?
Actually, let me be a bit more charitable than that. Let me guess that some artisans designed both sets of coins and simply didn’t foresee the vending machine problem (or parking meter problem, if you wish) because when the coins were designed, there weren’t a whole lot of machines that could appreciate coinage.
If we look at it in that light, then perhaps we shouldn’t be surprised that the same denominations have the same dimensions. The designers were simply being consistent, and fostering mutual understanding between our two great nations. Zowie!
It’s not necessary to tell us that, because we already know. The U.S. economy dominates ours. All we can do to “retaliate” (if that’s the right word) is to send cold fronts down to plague you. Oh, and we send you most of your decent comedians. So you win some and you lose some. We chill you with our frosty air, and warm you with laughter.