Yes, there are 3-way dimmers but you only use one on a 3-way set-up. 20 cans of any size is a bunch for a kitchen. IMO, you would be better served with fewer 6" cans which will give you more defused lighting. If you are determined to use 20 cans, I would break them into 3 circuits.

Most switches/dimmers are rated for 600 watts, so your total lighting load on that switch should be less than that. Since PAR20 bulbs typically are 50 watts, you could get 12 on there, but I'd do less. Also you could have one circuit but two switches. For flexibility I would be sure to have at least two different switch loops (e.g., control lights over one run of counter and the other counter separately).

3 way dimmers are available. As redhead says, one switch has dimmer other is just a switch. You can get fancy ones that remotely control the other dimmer so that both can dim the lights but I wouldn't bother.

Thanks for the replies.
We were set on the 4" cans, but I guess we will split the runs. Not sure how the dimmer will pan out, maybe just use plain three ways.
What about spacing of the cans. We have one wall which is 22' long, so we thought we will need 20 cans.
Is it possible we do not need that many.( the layout is posted in the lighting forum.

thanks again

I would suggest 2 circuits with different wattage CFL Par-20s in each. Then use each or both for two or 3 'scenes' without the use of dimmers and much more efficient lighting.

You might also look at Insteon switches and dimmers for easy installation of multi-way circuits without the wiring difficulties.

Oh, for 4" cans with 50w equivlent bulbs in kitchen working mode, 24 to 30" spacing works well with the light's centerline even with the front edge of the countertops. Center one over the sink, one over each major workstation and one over the fridge if its a sxs or french door.

jc, we will be putting pendants over sink which has a window and also a pendant in front of another window, do we still put a can in front of windows or is it better to place the cans in front of wall cabinets that are next to the windows?
So with a 22' wall we are looking at close to 10 fixtures at 24" spacing. is 30" spacing going to cut it so we can reduce number of fixtures.

thank you

Some kitchen.

lonesparky, yes it will be a large kitchen but not for our size family and the amount of entertaining we do. I hope what they say is true( large kitchens sell).Anyway still wandering about the lghting issues. We are real close to needing to make a decision on size, amount and spacing.
thanks