Tier 5 Visaholder (gaining US citizenship)

Hi, I am a Canadian citizen with a US green card. I recently was granted a Ter 5 visa on the basis of my Canadian citizenship so that I can join my boyfriend who is studying in London, and hopefully to work here as well. My Tier 5 visa is included in my Canadian passport, which is valid until the visa expires in 2 years. However, I had also applied for US citizenship before moving and my application is being processed. My family lives in the US, so I will need to visit them regularly, but will need a US passport once I become a citizen.
My question is this: obviously I don't want to forfeit my Tier 5 visa, so can the visa be transferred to my US passport on the basis that I am a dual citizen? I am not ruling out asking for a hold on my US citizenship application, but wanted to know if I have any other options. Thank you so much for your advice.

You visa can't be transferred to your US passport as you did not apply for the visa under that identity and nationality. But why are you hoping to do this? What's wrong with keeping your Tier 5 leave in your Canadian passport assuming your are not renouncing that nationality?

I agree with you completely as I intend to retain my Canadian citizenship. But one concern I have is which passport to use when. Obviously I will use my Canadian passport (as it contains my visa) when I enter the UK; but when I return to the US, I will have to use my US passport and it won't have an UK entry stamp. I am worried that this will raise questions with US officials. Am I overthinking this? Any suggestions?

It won't matter that you don't have stamps in your passport when you are being admitted as a citizen of that country where you have arrived.