You might want to try the touring forum -- it's more active than this one.
A truly beautiful ride is the going to the sun highway in Glacier park (US side), but it almost certainly won't be open as early as May. I biked it in early July and they had just opened it, with banks of snow making it seem like riding into an icebox. I've biked around Radium and other areas, but always far later in the year.
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Zero gallons to the mile