It seems to vary greatly. Just take care of her and don't worry.
I would start saving now for a 2nd gen, if you like the 1st like I did you will love the 2nd.

 

How an engine is cared for generally determines how far it will go. Generally depending on where you live rust will eat the truck up first.

 

As I posted, my truck is a 2004, 17 year old, no sign of rust, but I don't live where the streets are "more salt than asphalt". Except for a few little dings common from 17 year on the road, she is still is in pretty good shape.

 

When I got rid of my Canyon 2007 reg. cab 4x4 with all factory options at 42,000 miles it was still purring like a kitten. Cleaned the throttle body once (they seem to get gummed up over time on the !5 affecting the idle) and had the notorious passlock problem and had GM fix that. Should have kept the truck, loved it. But hell no had to have something different. Don't get me wrong I really like my 2019 LT 4x4 Z71 crew cab but for just me and my dog I really liked the smaller truck with the cloth bench seat I ordered in it. Nobody's even set in the back seat of my newer one yet

 

I have a 2004 Canyon with the five cylinder engine. It has 118,000+ miles. Does anyone have any idea how long the L5 will last? 150,000, 200,00? Also, if the engine goes bad, what is a good replacement. I love my little truck and thought if it ever needed an engine swap, I would go that route. Answers, anyone?

You could head over to the 355Nation forum for more info on the 1st generation Colorado.
I've been on there and here since 2005 and owned a 2005, ordered out a 2010 with the 3.7L I5 and now out 2017 2nd Gen Colorado.
The 2005 and 2010 are still in the family and running well. The 2004/5 did have some valve wear problems so watch for that. If you did want to replace the engine, maybe look into the 3.7L in +2007 model years. More info on that at 355Nation.

LINK: - - 3.5/3.7 swap?

 

As far as the engine goes, it should last well over 200,000 with good care and maintenance. Mine is sitting at 338k and runs better than most cars driven off the lot.