I agree with @rumtscho that you are unlikely to get the desired results from canned corn as you really probably need raw. If you do try canned, make sure it is whole kernel type and that might improve your results. If you cannot get fresh corn, frozen, uncooked corn might work, but even that is usually blanched which might be enough to change the results too much for your desired results, and I would again try for whole kernel, not cut.
Digging around a bit, I found a blog claim that a medium ear of corn yields an average of 3/4 cup of kernels. Ears of corn vary substantially in size, for a recipe that gives a measure in ears, not in volume or weight, I would immediately say that exact amount is not critical, you just need a very rough amount so I would use the 3/4 cup as being roughly correct. If weight works better for you, a cup of corn kernels should be about 4.5 ounces or 125 grams (from another blog http://www.veg-world.com/articles/cups.htm), so your three ears would be ballpark of maybe 275 grams with an assumption that exact measurement is not critical.
ETA from @Jolenealalaska, adding a part as creamed corn may very well get you some of the missing goodness in both canned and frozen corn. I might even try a higher cream corn ratio than their 3-to-1 suggestion. A bit of experimentation may get you close to your target.