Depending on the sconces chosen, they could provide sufficient light by themselves. If you really want can lights (4" or smaller) , take a look at the CREE LR 4 can lights for inspiration. They come with the housing and trim included. For a purely decorative purpose, you could look at low voltage 2" mr16 cans. Presumably, the lighting will be for the vanity area and not the shower/ tub section? Or do you intend to have can lighting over the shower/ tub section as well? An alternative to can lights could be cove lighting. - Thin light bars hidden by crown molding slightly lower than the ceiling. This can be accomplished using thin rigid led bars, rope lighting or fluorescent. That way, you don't have to create more holes in the ceiling. How do you intend to control the lighting? All from 1 or more switch(es)? Is dimming required/ important?

Not to change the subject, but there's analternative vanity we like that has two smaller mirrors, which would allow us to go for the sconces. The problem is that the top is a white carerra marble and we don't think it will go with the floor/wall tile we're getting. The vanity with the big mirror comes with a plain white top, which we know won't conflict with the floor and wall tile.

What about this light fixture? https://www.1800lighting.com/hinkley-lighting-fritz-24-inch-3-light-bath-vanity-light-CP75020.html https://www.1800lighting.com/hinkley-lighting-fritz-14-inch-2-light-bath-vanity-light-CP75001.html https://www.lightingnewyork.com/product/hinkley-lighting-clancy-bathroom-lights-5442bn-cl.html?utm_source=Criteo&utm_medium=Remarket&utm_campaign=Hinkley%20Lighting&utm_content=Wall%20Lights%20%3E%20Bathroom%20Vanity%20Lights&utm_term=5442BN%2DCL&vip=TEUW4WDC Hayneedle has a very similar mirror for around $24 less. https://www.hayneedle.com/product/aspirehomeaccentsmorseindustrialmetalwallmirror205wx33hin.cfm

The problem, of course, is that the bulb is tucked up inside the housing so the light is directed only downward. You could install something like the retrofit Halo SMD whose flat lens is slightly below the ceiling resulting in light dispersed in all directions, including reflected off the mirror. If you could remove the housing from the ceiling, you could replace it with a canless fixture such as this Juno WF6 or Halo HLBSL whose lens is flush with the ceiling. When you remodel you'll want to add fixtures on the wall. -- amateur