What did you do to try and fail to control the Japanese beetles? I don't think that I have ever seen a Japanese beetle, in person.

Last year, I used a cup of water with soap. I just tap them and they drop. I usually do this in the afternoon. If I do this in the morning, they'll fly. They're very harmless. However, there were tons of them this year that I just accepted that I lost the battle against them. It's not just the canna that they love. They also love my hollyhocks, 4 o' clocks, and zinnias. They ate my Ensete Maurelii(beside the cannas) but the damage was very small. I was really shocked that they did very small damage to the Ensete M. They didn't touch my sunflowers, russian sage. Oh, they also loved my dahlias.

I see very very few jap beetles now to almost gone. Looks like I'll have a nice flower on the bengal tiger. Also, the jap beetles didn't do a lot of damage to the leaves of canna australia or canna tropicanna black. They did ruin the flowers but not the leaves.

This is how they look like.
Japanese Beetles

If I were you, I would spray with Sevin at the first signs damage.

I was also told by a neighbor. How is it sprayed, is it sprayed on the plants or on the ground?

It is sprayed on the plants. Apparently, Milky Spore is applied to the ground to kill grubs. See http://forums2.gardenweb.com/forums/load/fruit/msg0616124625787.html

I have no experience with either.

Thanks for the info! :) I'll try sevin next year. I'll use 3oz/gallon. I'll make sure to watch them mid June. That's when I noticed they started to come out.