Looking for similar / alternative artists to westlife and backstreet boys  

Backstreet boys and westlife are great boy band. I recommend that you will try Michael Learns to Rock, The Journey, chicago, scorpion, and other like a1 or Nysnc.
Nowadays, new boyband doesn't last longer compare than that of the old one.
The older boy band have great music and they are still remembered how many years pass by. Their music can not be forgotten and really marked in every listeners and their songs seem new that doesn't go old even their is already new boy band.

Hi

Well there are backstreet boys and westlife members who have solo careers such as Nick Carter and Brian Latrelli from BSB and Brian McFadden from Westlife

Some similar bands are:

Nsync
98 Degrees
O-Town
Jesse McCartney
Five
Blue
BBMak
A1
New Kids On The Block
Boyzone
Hanson
Ryan Cabrera
Take That
A*Teens
Shayne Ward
Savage Garden
Gareth Gates
Duncan James
Michael Learns To Rock
D-Side
911
Steps
Busted
C21

Hope this helps :)

Well, they're not a dancing or stand up off stall kind of boyband, I'd argue that they're not a boyband at all personally, but you should really check out the band McFly. They have some great pop songs, especially from the years 2004 and 2006, and are extremely good live too. I recommend listening to the songs 'Sorry's Not Good Enough' and 'All About You' but they have many different songs. They've been a band for 6 years now :) Still going strong here in the UK! 7 number 1 singles and 2 number 1 albums here.

Another band quite alike which I'm sure you'd have heard of are Take That. Especially good in this second half of their career now they're in their late 30's (I think). Hugely successful! They were first around in the 90's.

Try 5ive. I know someone else recommended it, but it was one of the boy bands I loved when I was a little girl haha.