Personally I'd hold off. Although the slingbox a/v isn't "Officially supported" anymore they work just fine with all versions of desktop and mobile software including the iPhone. There is no real advantage (and it's been like this for a long time at this point) unless you're going to move up to the Slingboc Pro HD model (which adds HD streaming, and of course more inputs as well as an internal ATSC tuner).
As far as upgrading in canada to receive the 50 off, I can't really comment there; except that online retailers are at least $50 cheaper then slingbox's website; so what's the advantage of ordering from them again? Right now they are going for $174.23CN new including shipping on ebay.ca, or $159.95US new including shipping on ebay's .com US's site. Amazon also has it new for $148.99US with free shipping. None of these outlets charge tax as opposed to buying it from sling or a local retailer.
A WiFi hotspot is a "net" connection. I'm assuming you mean you have not been able to actually view it via a 3g connection...???
If that's the case, assuming you have AT&T since this is an iPhone 4 (unless you unlocked/jailbroke and are using it on T-Mobile), you should be able to view it as well. If not remove the iPhone app and reinstall it again.
If you are jailbroken or using T-Mobile (or any other gsm carrier for that matter), it might be a carrier issue or the fact that you may have the wrong data package update installed durign jailbreaking....
How about supplying some more info in order for me to get oyu up and running correctly.
What OS are you runing on your iPhone?
Are you in fact using AT&T?
Is this phone jailbroken and or unlocked; if so with which jailbreak firmware OS and which application did you use (greenpoison, etc)?
What version of the sling mobile app are you running?
What firmware version is your slingbox currently on?
Try those for starters....