It is a mistake to get into a business with a partner(s) without a solid, written partnership agreement. The agreement establishes important rules about how the partnership will operate, including:

• who the partners are, what role each partner will play,
• how much capital each partner will contribute,
• how profits and losses will be split between partners.

Even though the law does not make it mandatory to have a partnership agreement in place when two or more legal entities come together in business, it benefits you to have one in place. Without a solid partnership drawn with the help of a business lawyer, the potential for disagreements is high.
Again whether or not you have a partnership agreement in place, the law will assume that you have entered into one if your conduct as partners and available business accounts and documents meets the indicators of a partnership agreement under the Ontario’s Partnership Act.
The implication of an implied partnership agreement is that all profits, losses, and liabilities of the business are shared equally between partners. Again the potential for prejudice to partners is high if an ownership dispute ever made it to court.
If you are combining your knowledge, capital, or other resources with one or more legal entities with the intention of making a profit, that is technically a business partnership. A legal entity can be a person or a trust, or a registered business.
Drafting a partnership agreement with the help of a business lawyer ensures that the agreement is sound at law and that each partner’s role and responsibilities in the business partnership are clearly defined.
As every partnership is unique in what different partners are bringing to the business, the default rules that govern partnerships under the law do not always apply. Where they don’t, they can only be amended by a written agreement, which is why you absolutely must have one prepared by a lawyer who understands business law.