COS cancellation and accepting another offer

Hi Guys,

Anyone faced this issue before? Need your help on below and many thanks in advance. any ideas are welcome

- Accepted company A offer as I am on visitor visa and didn't wanna take risk
- They started applying Defined COS last two days ago
- Company B (xxxx - My dream company) is offering me this position and I invested around 8 hours interview for this and wanna get it. They will do background check now though and a couple of days will last.
Question is

- Will there be any issues if I reject company A now? there is employment contract signed so far and HR just shared draft only yet too.
- I am scared if company A refused to cancel COS and company B cannot apply.
- Should I tell company B openly about this? scared later if they find out later

Hi Guys,

Anyone recently got sponsored ship job from xxxx?
I recently finished program manager - final panel interview and pending result.
Upon application stage, I filled in "yes" on I need sponsorship though.

But I got another offer and have to reject that to accept this xxxx job.
I am scared, while xxxx is applying visa and if something happens and withdraw offer. Do they have bad reputation for that before as I been hearing lay-off news in past year.