Ever since adult-use marijuana was legalized in Canada, cannabis companies intensified their marketing campaigns to win investors. Nearly all players are boasting first-mover advantages that will ensure industry-leading positions.

However, only the top-tiered weed companies, Aurora Cannabis (TSX:ACB)(NYSE:ACB) and Canopy Growth (TSX:WEED)(NYSE:CGC), have real potential to claim market leadership. The rest of the cannabis companies know that the two giants are in a different league.

There’s a new green scene in downtown Lacombe as a total of four cannabis dispensaries are in the midst of opening.

Fuzzy Budz became the first to open last week, and will soon be followed by the opening of Merry Guanas on Thursday, Aug. 1, thanks to the Alberta Gaming Liquor and Cannabis (AGLC) Commission’s lift on the retail cannabis licence moratorium at the end of May.

The four stores, which also include Canna Cabana and MJAYZ Cannabis Corp., will actually give Lacombe and it’s 13,000 residents more cannabis stores than nearby Red Deer with over 100,000 residents.

Aphria Inc. has posted its first profitable quarter since the legalization of recreational cannabis, driven largely by revenue from its German distributing partner CC Pharma and significantly higher volumes of cannabis sales in Canada’s adult-use market.

For its fourth quarter, which ended May 31, Aphria generated net revenue of $128.6 million — an increase of 75 per cent from the previous quarter — while net income and adjusted EBITDA were both in positive territory at $15.8 million and $0.2 million, respectively.

The Leamington, Ont.-based company also exceeded most analysts’ expectations on a key indicator — the quantity of cannabis sold on the Canadian market.

The vast majority of cannabis stocks flat out wilted under the summer heat in 2019. Top dogs like Aphria, Aurora Cannabis, and Canopy Growth (NYSE:CGC) all saw their market caps take a whopping 20% haircut in just the past 30 days.

For investors looking for some good stocks to jump on board, the three below have all been doing well in July and could still have a lot more upside left.

Air Canada  (TSX:AC)(TSX:AC.B) is coming off another strong quarter where earnings came in above what was estimated for the airline. And despite being at 52-week highs, the stock has shown no signs of slowing down anytime soon. In just one year, the stock has doubled in value, becoming one of the hottest buys on the TSX.

When looked at over a multiyear stretch, the cannabis industry has delivered plenty of big winners. If investors had bought into a handful of the most popular pot stocks at the beginning of 2016, they'd be up a quadruple-digit percentage today.

However, the past four months haven't been pretty for cannabis stocks, with some folks suggesting that the marijuana bubble has (once again) burst. Supply issues throughout Canada have constrained the amount of marijuana products hitting dispensary store shelves, while high tax rates in the U.S. have fueled the black market, leading to declining sales and bottom-line projections almost across the board.

CannTrust Holdings shares rallied Wednesday to lead cannabis stocks higher, after the troubled company hired a financial adviser for a strategic review of its options, including a possible sale of the company.

CannTrust Holdings (TSX:TRST)(NYSE:CTST) stock has been plummeting ever since it was revealed that the company sold unlicensed cannabis and circumvented regulations for selling legal marijuana. The stock has shed over three-fourths of its value since March, and it doesn’t seem like the end is in sight just yet. 

Reports suggest that the company was cultivating and selling unlicensed cannabis from the date of legalization to early March 2019 at a Niagara greenhouse that only received appropriate licences in April. The discovery prompted Health Canada to suspend CannTrust’s licences, which means it can no longer sell the 5,200 kilos of dried cannabis it has already harvested. 

It has been quite a slippery slope for Canopy Growth (TSX:WEED)(NYSE:CGC) stock since late April. After hitting a record high that month, its shares have fallen more than 35% since then.

After a powerful rally during the early part of the year, the sell-off in marijuana sector has been drastic since April. Horizon Marijuana Life Sciences Index, for example, has fallen more than 25% since April 29.

So, what’s causing a sudden change in heart on the part of investors who have suddenly started to hate these market darlings? In my view, there are two main reasons behind the current sell-off.

It’s been a brutal summer for weed stocks. After opening the year on a high note, the marijuana sector began tanking in May with no end in sight.

Although the month of May was a weak one for the markets overall, marijuana stocks were among the hardest hit–and they continued falling after other equities began to recover in June.

If you’re going to invest in weed stocks right now, it pays to tread carefully. Now that marijuana producers’ fates are beginning to diverge, it’s more important than ever to pick the right ones.