Upvote:1
If both of your flights are on the same ticket, and you miss your connection despite doing the best to catch it, then United will re-book you free of charge to the next available connection to PDX. This may answer an implied question.
United would not sell you such a ticket if travelers tend to miss such a connection. They would lose money in the long run otherwise.
Having said that, 1h45 is not a lot, but often doable. If you are unlucky and stand in line for a long period of time at immigration, security is crowded, or you get a more thorough check at immigration, then you will however miss it (unless your second flight is delayed). There are a few things that you can do to reduce risk of missing your plane:
Try to get a seat more towards the front of the plane. In the majority of cases, the front door will be used for de-boarding.
Should your incoming flight be delayed, after de-boarding, move swiftly and try to overtake people on the walking way to immigration if this can be done in a non-rude way (often possible by, for example, taking the stairs next to escalators). There is nothing morally wrong with this approach if you have a tight connection.
Should there be a long queue before customs and time is running out, politely ask people in front if you may overtake, mentioning your tight connection.
Before going through security again, see if there is a member of the airline staff nearby and ask if she can put you more in front of the queue. They are allowed to do that. Of course, only do so if it becomes relatively obvious that you would otherwise miss your flight.
If 1-4 sound like stress to you: they are. But for the ease of mind, keep in mind that the airline should rebook you if you miss the connection due to unavoidable queues, even if you do not follow tips 1-4. Especially if you are travelling with children, tips 1-2 are not always doable.