Bryan Adams
Andrew McMahon (moreso when he was in Jack's Mannequin)
Justin Timberlake

Since legends like MJ, Stevie Wonder and Prince have already been named multiple times, I'll say:

Barry White
Phil Collins
Luther Vandross
Marvin Gaye
Geroge Michael
Lionel Richie
Michael Bolton
Freddie Jackson
Sylvester
Ru Paul
R. Kelly
Peabo Bryson
all the Bee Gees

can't narrow it to just a three sorry.....

Michael Jackson.
King Of Pop.
Applehead.

Justin Timberlake, Bruno Mars, and Usher.

Luther Vandross
James Brown
Marvin Gaye
honorable mentions: Alexander O'neal, Babyface, Al B. Sure

R&B: Luther Vandross, Wanya Morris and Usher.

Pop: MJ, Bruno Mars and JC Chasez.

Rock: Freddie Mercury, Myles Kennedy and Thom Yorke.

John Newman
Bruno Mars
Chester Bennington (Linkin Park)

John Mayer
Billie Joe Armstrong
Pierre Bouvier

Gavin DeGraw
Ryan Tedder
Chester Bennington

Oh, I'm late.

Justin Bieber, Conor Maynard, Usher

(I would include K-Pop acts, but meh, I can't really choose. All are perfect.

Gary Barlow
Shane Filan
Ronan Keating

Sam Smith.
Michael Mcdonald
Stevie Wonder.