It's not really a question of how marriage will impact your stay in the United States, but how that marriage to a United States citizen could impact your immigration status (i.e. what immigration benefits you may or may not be eligible for and why). You and your fiancée should sit down with an immigration attorney who could examine your immigration history and advise you on this topic.
If USCIS is interviewing you and your spouse for a second time, I would strongly advise you to retain an attorney who can accompany you to the interview. Generally, multiple interviews (or separating people during an interview) indicate an officer is concerned regarding the validity of a relationship and there could be allegations of fraud. If that happens it would be to your advantage to involve an attorney sooner rather than later.
Certain assets may also be used to help meet the affidavit of support requirements. An immigration attorney could examine your entire financial picture and possible options in meeting the requirements. Good luck!
I agree with my colleagues. You should consult with an immigration attorney before taking any action. You would want to gather the arrest report, any associated court documents, the terms of your diversion program and proof that you successfully completed the program. The attorney would want to review these items to properly analyze your case.
Initial review is, as the other attorneys pointed out, merely the beginning stages of the adjudication process. I understand this lack of information can be frustrating. An attorney could assist in explaining the petitioning process and time frame involved. It is unclear from your post whether or not you also filed an application for adjustment of status, which would also impact the processing of a case. Good luck.
Where to marry is a personal choice with many factors to consider- venue, cost, guests, etc. Whether you marry in the U.S. or Canada, be sure that the marriage is lawful in the place where it occurs. If you chose to petition for your Canadian spouse to immigrate to the U.S. you would need to establish that you have a valid and legal marriage regardless of where it occurred.
You may find the answer to your question at www.uscis.gov as USCIS maintains posted processing times for various petitions and applications (note that some cases go faster than posted processing times and some take longer). Today it indicates that the government is taking about 5 months to process these types of cases. You may also use the receipt number located on the notice you received to check the status of your case at the same website.
I would not recommend filing an application for adjustment of status on your own, as the consequences of a denial could be quite severe. If you are questioning where to file the application, it would be best if you consulted with an immigration attorney prior to filing anything to at least address risk/eligibility. If the employer's attorney is not representing you in this matter, seek another opinion. Good luck.