You can add raspberries now or wait until fermentation is done and rack it over the berries in secondary. Just be aware that raspberries tend to trap a lot of CO2 in them during refermentation, which can cause a big mess if you don't leave enough headspace.
I prefer frozen thawed fruit over the canned stuff as it just tastes better in my opinion. I've had the Oregon puree come out just fine, and sometimes there's a metallic, flat taste to it. Just smash the berries up a bit if you're using whole fruit. A week might be a little quick, though, and there will probably be a lot of fruit floating around assuming the yeast can get to all the sugars in them. I wait for them to turn white and start to fall, which can take around a month. Maybe quicker with a good cold crash. Puree should go faster, if you're ok with the flavor. Some people swear by it.