I live in Vancouver on a working holiday visa, from Australia. I got a waiver form to go to the states, but just went for a day at the beginning of the year. This was the 90 day waiver and then "expired" in the beginning of April. I want to go to Seattle for the long weekend and Disneyland in July. Do I have to get a different visa? Or can I renew my visa waiver that was the 90 day one? If I renew it how?
Since it has been more than 90 days since you last entered the US, and more importantly since you were only in the US for a day (and should have a passport stamp from returning to Canada that shows this), you should have no trouble returning for a holiday.
The 90-day rule you have read about is often misinterpreted. It is a rule intended to prevent visa runs to Canada and other nearby countries, so as to catch out people who are illegally trying to live in the US.
The terms of the VWP are very clear - it is only to be used for occasional, short visits to the U.S. If the CBP Officer thinks you are trying to "reset" the clock by making a short trip out of the U.S. and re-entering for another 90-day period, you can be denied entry.
Since you are a resident of Canada and have only spent one day in the US, you are obviously not trying to make a visa run and you will have little difficulty returning for another short visit.
The real question in your case is, what do you have to lose? The worst case scenario (and not all that likely) is that you will not be admitted. So you won't go to Seattle, but you'd simply be back in Vancouver. Other than missing out on a splendid city, nothing lost.
That said, your working visa in Vancouver might work against you - an immigration officer might think that you plan on working in the USA as well.