One of the nicest locations to get married in Kelowna is Bertram Creek Park (click link to be taken to their webpage). This is a park run by the Regional Distrist and you can make a reservation to use the park but it books up very quickly.
There are a couple different locations to have a wedding ceremony and both have spectacular views of Okanagan Lake. You can set up by the beach, which is beautiful, but just keep in mind you could get some noise from the passing ski boats and the general public will probably be in the area.
The second option is the amphitheater. It provides a little more privacy and it is much easier to decorate. With both locations you will need to provide your own chairs as well as an archway for the couple and the officiant to stand by.
A sound system is absolutely necessary as well. I've been to several outdoor weddings where you couldn't hear the officiant or the couple. Don't make that mistake! Get a good sound system and make sure you learn how to use it before the wedding and that you have someone to run it that knows that they are doing. Trust me, this is crucial. Bad sound can greatly reduce the magic and romance of an outdoor wedding.