I have a receiver that has as the only markings a serial number of No.136503
The original slide has the Pat. Dates and the Rampant Colt in the Middle.
The other side of the slide says Model of 1911 U.S. Army. I am trying to determine value so i can sell it here on the Canadian market. I believe it to be a Colt .45 Auto from 1916.

Any help would be very Much appreciated.

Thanks, JohnnyVolume

Johnny: Sounds like your receiver is missing some markings and your slide is mismatched. Yes, that is a 1916 serial number. In 1916 the rampant colt was still at the back of the slide, not in the middle.
If your receiver had the United States Property marking on it, the letters would be serif style. Your slide, with the rampant colt in the middle will have block style letters.
Hard to say about value without more specific info and perhaps some photos. But from what you say, value would be modest. With the missing markings and being mismatched, that really hurts collector value. But as a shooter, it's probably just fine.

JV,

It's a bit difficult for me to place value on your Colt, not only because of the lack of pictures but also I'm not sure what market conditions are like in Canada. Here in the USA there are enough ex-GI pistols floating around that only the original-condition specimens usually become collectible. But in Canada they may be sufficiently rare that anything with all-GI parts might be worth more than an equivalent example in the USA.