That looks identical to the Sportour that my brother owns, down to the blue cable housing. Unfortunately, he's not really a bike person and treats it with horrifying neglect, but it's very nice bike (I am SO buying it off of him once he graduates college and won't need it, if it survives that long...).
It's hard to tell from your pictures if the rear cluster is five or six speeds. My brother's Sportour has a 6-speed Shimano Uniglide freehub. If it is a 5-speed, I'm going to guess that yours is a couple of years older, from somewhere between 1980-82 (my brother's bike is an '81-'83, I think). The drivetrain is also different; my brother's bike probably came with Suntour ARx components, though it's difficult to tell because the front shifters and derailer were upgraded at one point to Shimano 600. I'm told that the Suntour equipment was probably OEM, but it's not really entirely certain.
"Sunshine" is just a brand name that Sansin used for selling their hubs in the USA. This is more evidence that this is a very early 80's bicycle. By the mid 80's, the stigma associated with Japanese bicycle components was long dead, and Sansin sold their hubs under their own name (my 1986 Miyata came with Sansin sealed bearing hubs).
The Sportour is a very nimble, fun bike to ride. Enjoy it!