On the second of November I'm going from Sweden to the USA with a stopover in London. I'm planning on bringing a cut roses bouquet with me and wonder if that's possible or will there be any problems?
If you do it properly, yes.
When traveling, assume anything that can contain bugs should be reported to the Customs Authorities.
Can I bring cut flowers for myself or significant other?
Most cut flowers are able to enter the United States. However, they must be declared and able to be inspected by an Agriculture Specialist. If the plant material is found to be propagatable or bug and disease agents are present the plant material will be seized and denied entry.