Hello! That sounds like an amazing trip through the Pacific Northwest. Here are some travel tips for your visit to Seattle, Portland, and Vancouver.

Best Time to Visit:
The best time to visit these cities is from June to August when the weather is warm and outdoor activities are aplenty. However, keep in mind that this is also peak tourist season. If you prefer a little less crowd, consider visiting in the shoulder months of April-May or September-October when the weather is still pleasant.

Route and Accessibility:
Your itinerary spans across two countries - the United States and Canada. You could start with Seattle, move south to Portland, and then head north crossing the border to Vancouver. Direct flights are available to Seattle from most major cities. From Seattle to Portland, consider a road trip down the I-5 or take an Amtrak train. For the trip to Vancouver, you can either drive or use the Amtrak service again.

Accommodation and Booking:
You'll find a variety of accommodations, from budget-friendly to luxury hotels in all three cities. Airbnb is also a popular choice and allows you to book entire apartments for your stay. Book well in advance, especially during the summer tourist season.

Clothing and Essentials:
Pack lightweight and comfortable clothing for the daytime during summer, but don't forget a jacket or sweater for nighttime or unexpected rain showers. Walking shoes are essential as you would be doing a lot of exploring on foot. Also carry sunscreen, sunglasses, and a reusable water bottle.

Health and Safety:
Standard travel insurance is recommended. Food and water are considered safe. Just stick to the general safety rules that apply to any urban areas. Watch out for your belongings and keep an eye out for any suspicious activity.

Local Etiquette and Respect:
Seattle, Portland, and Vancouver are friendly and diverse cities with a laid-back vibe. In general, people appreciate politeness and respect for the environment. Try to engage in local practices like recycling and composting.