The replacement battery that Lexus (and Toyota) dealers sell, in the US and probably Canada too, is made by Johnson Controls. I'd expect a similar lifespan to that Interstate battery from Costco you were considering.

The original battery in your car was likely a Panasonic. In addition to terrific durability, those Japanese Panasonic battery have translucent sides so you can see the electrolyte level without removing vent caps.

 

My 2010 IS350 came with a Lexus branded battery that lasted about 4 years. I changed it before it died, it was starting to crank slow on cold starting. Probably would have given me another 2 to 3 months. Now I have a Costco Interstate battery for almost a year